Search

The stomata of Ginkgo biloba L. are haplocheilic and perigenous, as described and confirmed by Pant & Mehra in 1964, but there are several striking differences in the structure of the stomatal apparatus between their descriptions and the findings recorded in the present paper. According to the present observations, the stomata are amphicyclic (usually incompletely), not monocyclic as they stated. There are 5 to 7 subsidiary cells (not 4 to 6); and a clear distinction into lateral and polar subsidiary cells is visible during most of the developmental stages at least, a fact that was not mentioned by Pant & Mehra. The papillae of the subsidiary cells arise from the outer free walls, not from the inner (centripetal) walls as they claimed. Further, these papillae do not conceal the stomatal pore as completely as was indicated previously: they extend only partially towards the opening of the epistomal chamber. These and other differences from published accounts are dealt with briefly and commented upon in the paper. Some notes are also included on the occurrence of amphistomatic leaves, and on the occurrence and nature of twin stomata.

Angola has previously received little attention from marine phycologists. Thirty known papers mention marine macro-algae and together list less than 50 species. This paper deals with the results of a survey carried out during January and February 1974: the number of reported species is now more than doubled. The species characterizing the littoral zones of rocky shores in this country are largely also to be found along the Guinea Coast, although minor variations do occur. The affinities of the Angolan marine algal flora are overwhelmingly with the Gulf of Guinea flora; there is a small but distinct transitional element, such as Plocamium beckeri, P. suhrii and Acrosorium maculatum, confined to localities in the south of Angola.

SUMMARY. 1 The paper deals, though far from fully, with the effect of settlement in New Zealand in regard to the primitive vegetation, and it may also be considered a supplement to Part III. of ‘The Vegetation of New Zealand’, ed. 2. 2 Taken, as a whole, the paper is an explicit denial of the mischievous biological belief, even yet common, that in the ‘struggle between the indigenous and exotic elements of the present flora the latter element is all-powerful.’ 3 According to the most recent estimate, the flora of New Zealand consists of 1850 species, 427 groups of species-hybrids, a great many varietal hybrids, and 650 exotic species. 4 In respect to the vegetation, the following terms used in the paper are defined:–primitive, modified, induced, and the last embraces indigenous-induced, exotic-induced, mixed, and artificial. 5 Competition between the indigenous and the exotic elements is far less severe than is usually considered, each element consisting mainly of different classes of life-forms, and each element for its greater part restricted to a different group of edaphic habitats, the indigenous to those of undisturbed soil, and the exotics to those of greatly disturbed soil. 6 Altitude also plays an important role, the exotics being essentially species of the lowland belt and decreasing both in numbers and power of attack with increase of altitude. 7 The struggle between indigene and exotic is very rarely an equal one, for the latter is generally greatly aided by the introduced grazing and browsing animals, nor must it be forgotten that such were wanting in primitive New Zealand. 8 The exotics have entered into no part of the primitive vegetation–rock and aquatic communities excepted. 9 Where the balance of nature in the primitive vegetation has been upset by the direct or indirect actions of man, a number of indigenous species have broken their bounds and become weeds equal in that undesirable status to any that have been introduced, Pteridium esculentum and Leptospermum Scoparium being indeed worse. 10 This matter of observing indigenes becoming weeds is of particular scientific interest, for the origin of the weed-host of Europe must surely be wrapped in obscurity. 11 Amongst forest-weeds an outstanding class is those which cut off a large part of light from the ground and inhibit, or make difficult, the establishment of seedlings which can develop into trees. 12 Tree-ferns and semi-tree-ferns belong to the above class, and it is shown how certain of these increase greatly by vegetative means, a fact hitherto unpublished. 13 In addition to indigenous-induced weeds there are many indigenous-induced communities, a number of which were unknown in primitive New Zealand, and a selection of such cases forms an important part of the paper. 14 Particularly interesting is the example where a forest, not greatly different from that of the neighbourhood, is being established on heaps of gtavel, stones, and silt (gold-mining tailings) in competition with exotics. 15 A few cases are discussed of indigenous species entering into and eradicating powerful exotic-induced communities, e.g. that dominated by gorse and broom being invaded by rain-forest species, including tree-ferns. 16 Another unexpected example–but now quite commonplace–is artificial pasture of European grasses and clovers being transformed into one dominated by an indigenous grass (Danthonia pilosa), such a community being unknown in primitive New Zealand where D. pilosa must have been not particularly common. 17 Still another example is the invasion of an induced-mixed, heavily-grazed pasture by Aciphylla Colensoi, once a highly-important member of montane low tussock-grassland, but now greatly reduced in numbers by fire.

In an earlier paper, which includes pollen descriptions for 93 genera and approximately 430 species of the large tropical family Annonaceae, the author laid the foundation for a generic reclassification and natural phylogeny of the family based largely on comparative palynology. The present paper includes generic pollen descriptions for an additional 12 genera and 18 species of Annonaceae.

SUMMARY From a consideration of the problems of plant-distribution, the writer is led to regard the history of the Angiosperms as resolving itself into two principal eras:— The era that witnessed the rise of the great families, a period of relatively uniform conditions.The era that witnessed the differentiation of these family types in response to the differentiation of the climatic and other conditions. It is argued that conclusions drawn from the prevailing influences now in operation could only be applied to the differentiation of the ancient family types–that is to say, to the second era in plant-history. It is not possible, so it is held, to apply a theory based on the present to an age of other things, other ways, and other conditions. Only the hypothesis that finds its guide to the past in the abnormalities of the present can be of service to us in the interpretation of times so different. The subject is introduced by a reference to two papers, contributed to the ‘Journal of the Linnean Society,’ which have an important bearing on the subject, the one by Bentham on the Compositæ, the other by Huxley on the Gentians. Then follows a statement of the differentiation hypothesis which involves the differentiation of primitive world-ranging types in response to the progressive differentiation of their originally uniform conditions. Allusion is then made to the dilemma into which all theorists fall when they come to handle the larger groups, the very persistence of which in our own age depends on the stability of their essential characters. If stable now, why so unstable then? We are thus forced to the conclusion that in the distant era that witnessed the deployment of the Angiosperms instability prevailed. It was an age of mutations, free and unchecked, and an age of uniformity of conditions, the mutability decreasing and the modifications becoming more and more fixed with progressive differentiation of conditions, an explanation suggested by a perusal of the accounts by Dr. Willis of his prolonged investigation on the Podostemaceæ. The distribution of families is then treated statistically; and it is shown that whilst they largely ignore the cleavage of the land into two great masses diverging from the north, they respond in a marked degree to the differentiation of the climatic zones. Behind their disregard for the present arrangement of continents and oceans lies the story of the first era, and behind their ready response to climatic differentiation lies the story of the second era. In the circumstance that the response made to the bi-cleavage of the land-mass is absent or small with the larger groups and becomes greater and greater as we go down the differentiating scale until it attains its maximum in the species, is recognised the contrast of conditions between the pre-differentiation era and the era when differentiation reigned supreme. It is held that there is a method here disclosed that could only arise by the family differentiating into the tribes, the tribe into the genera, and the genus into the species, since the opposite method of commencing with the species would produce chaos. The paper ends with the application of the statistical treatment to the larger groups behind the families, and it is shown that whilst the Dicotyledons display a much greater tendency to detachment from the tropics than the Monocotyledons, the Sympetalæ stand foremost in this respect amongst all the groups of the Dicotyledons. It may be added that there is a large amount of material in the ten tables which from considerations of space could not be discussed. These data have therefore to tell their own story

Further material of Gibasis geniculata (Jacq.) Rohw. (syn. Tradescantia geniculata Jacq.) and other Gibasis species collected in the field has been studied. The existence of several species in our earlier experimental material is confirmed. These include G. geniculata itself (2n= 32 or 48 small chromosomes), G. oaxacana D. R. Hunt (2n= 16 small chromosomes) and G. schiedeana (Kunth) D. R. Hunt, which has two chromosome forms, 2n= 10 and 2n= 16, both with large chromosomes. These forms are diploid and tetraploid based on x= 5 and x= 4 respectively and show a Robertsonian relationship with each other. The cytology of tetraploid (2n= 20) G. karwinskyana is confirmed and that of a diploid form (2n=10) described. The recently described G. consobrina D. R. Hunt (2n= 20) is shown to be cytologically comparable with G. karwinskyana, but to differ in significant details. Next, the cytology of G. pulchella (Kunth) Rafin., the type species of Gibasis, is described and also that of the allied G. matudae D. R. Hunt. Both G. pulchella (2n= 10, 15) and G. matudae (2n= 10) show interchange heterozygosity, with complete rings of ten chromosomes at meiosis in some plants of G. pulchella. Preliminary comments are made on the cytology of G. aguensis (Standl. & Steyerm.) Rohw. (2n= 10), another ally of G. pulchella, and on the G. linearis group, where the basic number appears to be x= 6 but two karyotype patterns have been found. A discussion of chromosome architecture in Gibasis in relation to the taxonomy of the genus concludes the paper.

The structure of the leaf epidermis of Bombax ceiba L. is described. Leaves of this plant have been generally reported to be hypostomatic. The present paper reports that on the upper epidermis up to eight rows of stomata are present along either side of the midrib. Development of the stomata is typically of the mesogenous anisocytic trilabrate type, but tetralabrate initials are also reported.

This paper assembles and, so far as is possible without extended field and herbarium studies, examines critically the validity of records of marine and brackish-water Chlorophyta and Xanthophyta for the western coast of tropical Africa. The whole mainland coastline from the northern boundary of Spanish Sahara southwards to the southern boundary of South West Africa, the oceanic islands from the Salvage Islands southwards to Ascension, and all islands close to the African mainland coast are included in the area covered. Each species entry includes all traced records for the species, the names which have previously been applied to it in the area, and additional comments or evaluation, where necessary. Comments have also been made at generic level in some difficult cases.

This paper gives the descriptions, habitats and distributions of 16 species of Euphrasia found in North America. The introduction contains a historical account of the discovery and treatment of these species and an account of their morphology, breeding biology, parasitism and species concept. A conspectus of the classification and an artificial key to the species is included.

The stomata in Gnetum ula Brongn. occur in large numbers on the abaxial surface of the leaves and are orientated in various directions. A few were seen in some preparations on the adaxial surface also, especially in the region of the midrib. Stomatal development follows the syndetocheilic type of Florin. According to the terminology of ontogenetic types suggested by Pant, they may be described as mesogenous dolabrate; they are mesoparacytic (rubiaceous) and amphicyclic. In this respect, and in several details, the present findings support the observations of Takeda, and differ rather widely from those of Maheshwari & Vasil. Twin stomata were also met with frequently, as well as several stomata lying together contiguously. The structural features of these are described and commented upon briefly in the paper.

The present paper deals with the anatomical description of five taxa belonging to the genus Fuirena. These can be divided into two groups: (i) F.wallichiana and F.umbellata; with short, cubical silica-cells each containing one or two cone-shaped silica-bodies, and (ii) F.uncinata, F.ciliaris and F.pubescens var.pergamentacea, with long silica-cells each containing two to six silica-bodieS. Further distinction at the specific level is possible on the basis of the presence or absence of wedge-shaped silica deposits, the nature of the anticlinal walls, the outline of the inner stomatal pore and the size of the inter-stomatal cellS. A characteristic type of stoma revealing an inner astroporous condition is also reported. A key based on the characters visible in the surface views of leaf is presented.

The flower pigments of Symplocarpus foetidus (L.) Nutt., a sapromyophilous plant were examined and cyanidin-3-monoglucoside, cyanidin-3-rutinoside and peonidin-3-rutinoside were identified. The pigments were identified by means of paper, thin-layer and gas chromatography.