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Cytological and histological studies were conducted on cotyledonary shoots of leafy spurge (Euphorbia esula L.) after the removal of the epicotyl. Growth owing to cell elongation was observed as early as 4 h in the proximal part of the shoot. Nuclear divisions were present in the distal part of the shoot and were not affected significantly by decapitation. They did not contribute to the early increase in length of the shoot. An increase of mitotic activity after 40 h and of shoot length after 72 h was observed; the latter was interpreted to be due to shoot xylem connections with the hypocotylary stele.

The mature awn of wild oats (Avena fatua L.) is geniculate consisting of a proximal twisted portion and a distal subulate awl; the awl is placed at right angles to the proximal part. The proximal part of the awn can untwist upon wetting with water and twist upon drying. The awl by itself cannot twist or untwist, but it can rotate along with the proximal part of the awn. It can, however, act as a brace causing the wild oat lemma-covered caryopsis to turn in the opposite direction dislodging it from the spikelet. The proximal part untwists on wetting to become straight when the two ridges of the awn, wide adaxial and narrow abaxial, become obvious and remain superimposed alternating with adjacent furrows. The two ridges internally are joined by a vertically extending thin sheet, three to four cells thick, called the connective. The ridges and the connective in a mature dry awn contain unlignified, thick-walled fiber cells which are individually capable of twisting upon drying and untwisting upon wetting. The short fiber cells of the connective, especially the ones centrally situated, undergo longitudinal compression with little or no twisting. The more peripherally placed fiber cells are long and tend to twist extensively and (or) form helices. The extent of longitudinal compression owing to the loss of water decreases in cells from the center to the periphery, but the twisting of cells increases. These differences in the pattern of shrinkage between central and peripheral cells of the awn result in a change of form of the awn from a straight to a geniculate condition.

The radial elongation of epidermal cells of the scutellum of wild oat (Avena fatua L.) embryos was studied quantitatively. In the nondormant embryos, the length of these cells, both on the adaxial and abaxial sides of the scutellum, was doubled in 10 days after the beginning of the imbibition of caryopses in water; no such elongation of cells was observed in the dormant embryos. The epidermal cells elongated to form papillae only after the primary root had emerged from the caryopsis. The length of the entire scutellum and that of its epidermal cells increased significantly in the presence of gibberellic acid and glucose or sucrose. It is suggested that the epidermal cell elongation is a postgermination phenomenon involving absorption and transport of the products of starchy endosperm hydrolysis, thus promoting further growth in the germinated embryo of the wild oat.

Detached leaves of Echeveria elegans were cultured aseptically on White's nutrient medium containing Na2SeO4 or Se-methylselenocysteine or S-methylcysteine. Both organic and inorganic selenium compounds had a greater inhibitory effect on leaf regeneration than the organic sulfur compound. While the callus formation appeared to be normal, the selenium compounds had considerable inhibitory effect on organogenesis. The sulfur compound was observed to be inhibitory at higher concentrations. Present results suggest that Se-methylselenocysteine inhibits organogenesis in E. elegans, a nonaccumulator.

Some observations and experiments were carried out on inflorescences of wild oats, Avenafatua L. (Poaceae). Results of these studies indicate that the distal spikelets are initiated and mature earlier than those in the proximal positions. In each spikelet, the primary floret matures earlier than the secondary floret. However, the less mature secondary floret drops from the spikelet sooner. The awn in mature florets is geniculate and shows a characteristic twisting movement depending on the availability of moisture in the atmosphere. The movement of awns results in periodic dislodging of mature florets from spikelets. The basipetal maturity of spikelets in the panicle, the acropetal maturity of florets in each spikelet, and the premature separation of florets aided by the awn movement produce caryopses of variable maturity and are of considerable significance in the reproductive biology of wild oats.

The persistence of Asclepias syriaca L. as a weed is related to its ability to propagate vegetatively by the development of adventitious buds on roots. These root buds arise on the main root and upper lateral roots within 25 days of the establishment of seedlings and are generally associated with the bases of lateral roots. A study of root anatomy shows that the origin of these buds is endogenous, in the pericycle and (or) its derivatives. No root buds are initiated until after lateral roots have developed and some cambial activity has begun. Vascular connections from the bud to the stele of the parent root, or an associated lateral root, are made at an early stage of bud development.

Growth and xylem differentiation in cotyledonary shoots were studied by partially isolating one shoot surgically in nondecapitated and decapitated flax plants (Linum usitatissimum var. noralta). Three types of cuts were made. The first type separated the shoot from the hypocotyl and the second from the epicotyl. The third type of cut was made at the node separating the two shoots, which, however, remained independently connected with the hypocotyl and epicotyl. In nondecapitated plants, the lateral shoots were inhibited. They had at their bases primary xylem strands, some of which were connected with the hypocotylary stele; the strands contained predominantly tracheids. In decapitated plants, the separated shoot grew vigorously when it was connected with both hypocotyl and epicotyl or hypocotyl alone. Such shoots contained at their bases abundant secondary xylem strands which were connected with the hypocotylary stele; the strands included predominantly vessels. The shoot that was isolated from the hypocotyl but connected with the epicotyl was inhibited even though it had abundant secondary xylem strands at its base. Results of this study suggest that growth of the cotyledonary shoot is dependent on the prior development of adequate xylem connections with the hypocotylary stele.

Avena fatua L. (wild oats), an introduced annual, is a successful weed in the cultivated fields of the Canadian prairies. Its inflorescence is a determinate panicle consisting of many spikelets, each of which contains two or three florets. During anthesis, the lodicules in each floret swell after water uptake and cause the lemma to diverge and to establish a wide angle between it and the palea. The essential organs in the floret are exposed to the environment and subsequently the anthers dehisce releasing pollen. The pollen grains are dropped on the stigmatic branches, thus effecting self-pollination. Following pollination, the floret closes because of the collapsing of lodicules. The pollen on the stigma germinates after the floret has closed. Anthesis, both in the field and in the growth cabinet, shows a daily rhythm and occurs in the afternoon. This rhythmic floret opening seems to be temperature sensitive. The ambient temperature range for anthesis in the field is 25–28 °C. The wild oat is primarily a chasmogamous species and enforced cleistogamy in the florets can be induced experimentally.

In both indeterminate long roots and determinate short roots of Euphorbia esula L., the promeristem usually consists of three meristematic layers. One of these represents the stelar pole, the second is continuous with the cortex, and the most distal appears to initiate the root cap – epidermis complex. Variations in this pattern are noted. Autoradiographs of apices of roots supplied with thymidine-H3 under field conditions demonstrate the existence of a region of low nuclear incorporation during a 24 or 48 hour period at the summit of the root axis in long roots. This region corresponds to the quiescent center described by previous authors. Short root apices consistently lack such a region. The pattern of nuclear incorporation of thymidine-H3 suggests that cell division is infrequent or absent in the center of the apex of long roots but not of short roots. Quiescence is thus a phenomenon which is superimposed upon the organization of the root apex in this species, and its presence or absence seems to be related to the developmental potentiality of the root. In many long roots the size of this quiescent region exceeds that of the region which may reasonably be designated the promeristem.

A laser pulse of 15 millijoules was used to rupture the wall of the target cell of the protonema of the moss Bryum stenotrichum C.M. and cause the protoplast to be ejected. A technique for isolating cells from an organized system, such as a moss protonema, by the laser beam is described. The behavior of the isolated apical and subapical cells in culture has been compared.

Entire detached leaves (L30 and older) and leaf-halves of Echeveria elegans Bgr. were cultured aseptically on an agar medium to study their regenerative capacity. The entire leaves with their bases intact produced shoots and roots regardless of whether they were placed erect, inverted, or flat on the medium. Similar leaves with their bases severed and placed erect produced roots from their cut ends. The proximal leaf-halves showed a regeneration pattern similar to the entire leaves depending on, of course, whether the leaf bases were cut or not. The regeneration in the distal halves was identical to the proximal halves whose bases had been removed. In the inverted position, a few distal halves and proximal halves with their bases removed produced shoots and roots. In all leaf types, inverted, erect, or flat, the regeneration occurred at the proximal end and in some exceptional cases, roots were formed at the distal cut end too. In general, the regeneration potential appeared to be much greater in the proximal parts than in the distal parts of detached leaves and the anatomy in the former was more favorable for regeneration than in the latter. Cutting the leaf base altered the regeneration pattern in the detached leaf but it did not have any effect on the capacity for regeneration to produce differentiated organs. The leaf fragments showed strict polarity in shoot formation which occurred only in the proximal region. The roots, on the other hand, appeared at proximal and distal ends.

The significance of Euphorbia esula L. as a weed is related to its capacity to persist under adverse conditions and to its mode of reproduction. In both these properties, the root system plays an important role. The root system is initially established by seedlings. The seedling has a vigorous primary root with extensive longitudinal growth and considerable cambial activity. Such a root has been designated a "long" root. By contrast, the first lateral roots produced on the primary root have limited growth and no cambial activity. These roots have been termed "short" roots. Thus, the seedling exhibits a "heterorhizic" pattern. Lateral long roots also arise on the primary root of seedlings but their origin is delayed until cambial activity has begun. Such lateral long roots arise much earlier on seedlings growing in denuded areas than on those growing in areas covered by dense vegetation. The mature root system is described in terms of horizontal and vertical long roots, which make up the conspicuous framework of the system, and of the short roots which they produce. Long roots produce shoot-buds and the origin of these structures is delayed until cambial activity has started. Short roots do not give rise to shoot-buds. Cambial activity in long roots appears to be connected with bud production and its absence in short roots probably underlies their inability to produce buds.L'importance de Euphorbia esula L. comme mauvaise herbe est connexé a son capacité de persister dans les situations hostiles et à sa methode de reproduction. Dans ces deux caractéristiques, le système des racines a une signification profunde. Initialement le système des racines s'établit dans le semis. Le semis a une racine primaire très forte avec beaucoup de croissance longitudinale et avec une activité considérable du cambium. Une racine de cette espèce s'appelle une "longue" racine (long root). Par contre, les premières racines latérales que poussent sur la racine primaire ont croissance limité et aucun activité du cambium. Ces racines s'appellent les "courtes" racines (short roots). De cette façon, le semis montre un dessin "heterorhizique" (heterorhizic). Les longues racines latérales ont aussi leur origine sur la racine primaire du semis, mais l'origine est retardé jusqu'au commencement de l'activité du cambium. Les racines de cette espèce apparaissent beaucoup plus tôt sur les semis qui sont situés en terre sans autre végétation, que sur ceux qui sont situés au milieu des autres plantes. Le système adulte des racines se décrit sous forme des longues racines de l'espèce horizontale et verticale, lesquelles constituent la charpente bien visible du système, et des courtes racines que sont produites par les longues racines. Les longues racines produisent les bourgeons, mais l'origine des bourgeons est retardé jusqu'au commencement de l'activité du cambium dans les racines. Les courtes racines ne produisent pas les bourgeons. Il paraît que l'activité du cambium dans les longues racines soit corrélative avec l'initiation des bourgeons et l'absence du cambium dans les courtes racines explique probablement leur incapacité à produire les bourgeons.

Excised leaves, L1–L30, of Echeveria elegans Bgr. were cultured aseptically on an agar medium to study their regenerative capacity. The younger leaves tended to produce roots earlier than shoots and some had not produced shoots by the time of termination of the experiments. The older leaves produced shoots earlier than roots and in such instances the shoots appeared on the adaxial side. In no case was the appearance of shoots on the abaxial side of the leaf noticed and this suggested the possible manifestation of polarity of regeneration. The leaf regeneration to produce roots or shoots depended on the degree of vascular differentiation, particularly at the leaf base where regeneration normally occurs. In young leaves that had little or no vascular differentiation at the time of their isolation, abundant callus appeared in which the first primordia initiated were of roots. The old detached leaves had short petioles, which contained mature vascular tissue, and produced very little callus in culture.

The apex of leafy spurge (Euphorbia esula L.) has a stratified mantle and a subjacent core. The mantle of seedling shoots had two to four layers and that of the adventitious shoots developed on roots had three to eight layers. Results obtained from an analysis of the mantle carried out with reference to the mitotic activity indicated a greater frequency of divisions in the peripheral parts where the leaf primordia are initiated than in the middle part of the apex. The adventitious shoots that are normally determinate in their growth potentiality develop an extensive layering in their apices. The shoot apices of the seedlings, which have a more prolonged growth, show much less stratification than those of the adventitious shoots.

A survey of dicotyledonous species of the prairie and forest regions of southern Saskatchewan disclosed the occurrence of 38 species (12 introduced, 26 native) which produce adventitious buds on their roots.

Histological analyses of adventitious shoot apices of leafy spurge (Euphorbia esula L.) showed variation in the number of mantle layers at various stages of development. The older shoots (stages III and IV) tended to have a larger number of mantle layers than the younger ones (stages I and II) some of which contained two or three layers. The procambial differentiation was acropetal extending from the axis into the leaf primordium and the same pattern was noticed in all stages of development of adventitious buds and shoots. The shoot apex contained larger nuclei and nucleoli in the midsector than in the peripheral sectors and the nuclei in the former had fewer nucleoli. The total volume of nucleoli per nucleus was more in the midsector than in the peripheral sector. However, the ratio of total nucleolar volume to nuclear volume was very similar in all the sectors, suggesting uniform metabolic activity in the adventitious shoot apex.

Analysis of apices at four different developmental stages (progressively older from I to IV) of adventitious shoots of leafy spurge (Euphorbia esula L.) was carried out. In this study, some selected histochemical and autoradiographic techniques were used to study DNA, histone, and RNA changes during vegetative shoot growth. In the early vegetative phases (stages I to III), the DNA distribution and DNA synthesis based on Feulgen stain and thymidine-H3 incorporation respectively were found to be greater in the peripheral sectors (S1 and S3) than in the midsector (S2) and consequently the apex showed a characteristic cytozonation. The central zone (S2) showed less DNA staining and the rate of DNA synthesis was slower than that in the peripheral sectors. This central zone, which is often considered as méristème d'attente, cannot be interpreted similarly for there was slow DNA synthesis as indicated by the low incorporation of thymidine-H3. It is suggested that the nuclei in S2 in stages II and III had a longer mitotic cycle than those in S1 and S3. The zonal pattern seen in the early stages disappeared in stage IV. This final stage may be considered as the "intermediate phase" during the transformation of the vegetative apex to the floral apex. The distribution of nucleohistones based on results of alkaline fast-green staining procedure was similar to that of Feulgen stain for DNA at all four stages. However, when lysine groups in the histone were blocked by acetylation method, the apices showed that the arginine-rich histone fraction was dominant and uniform in all four stages. This means that in stages II and III, S2 had less lysine-rich histone fraction than S1 and S3. The nuclei in S2 in stages II and III had longer mitotic cycle and this was probably due to less lysine-rich histone content. The cytoplasmic RNA observed by following pyronin Y – methyl green staining method and RNA synthesis based on uridine-H3 incorporation showed no sharp differences among the three sectors of the apex in all four developmental stages. It is interpreted, therefore, that the central zone (S2) in the apex was, although slow, quite active metabolically during the development of the adventitious shoot.

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