Search

The DNA base compositions of 60 strains of Scenedesmus were determined and found to be a valuable indicator for the differentiation within this genus (except for the very closely related species of the subsect. Desmodesmus). The range for all Scenedesmus species was 49.9-69.3 mol% GC for nuclear DNA and 36.8-39.9 mol% GC for chloroplast DNA. The separation of the genus Tetradesmus cannot be verified by GC values, because S. obliquus and S. (' Tetradesmus') wisconsinensis have a similar GC content. S. (' Chlorella') ultrasquamata, S. costato-granulatus (sect. Costato-granulati) and S. lunatus are separated clearly from all other species of the genus because of their high GC content. [ABSTRACT FROM AUTHOR]

Light and first SEM observations on the pollen of Aegialitis indicate that the two species of the genus are clearly distinguishable from all other genera of the tribe Staticeae to which Aegialitis presently is relegated. Intraspecific exine or aperture dimorphism which appears frequently in this tribe, is not recorded in this genus. A. annulata and A. rotundifolia have distinct monomorphic pollen and show a great resemblance in exine features with the tribe Plumbagineae, particularly species of Plumbago. Considering these and other features, separate subtribal status for Aegialitis within the Plumbagineae is proposed. [ABSTRACT FROM AUTHOR]

Sporogeneses and gametogeneses in Cordia sebestena are described. Anther wall develops according to the Dicotyledonous type. Pollen grains are three-celled at the time of dehiscence. The occurrence of enlarged, precociously developing, densely cytoplasmic cells toward the proximal end of the anther and between adjacent pollen sacs is a unique feature in this species. The possible functions of these cells are discussed. A placental obturator develops simultaneously with the ovules. The dual origin of parietal tissue (from nucellar epidermis and the archesporial initial) is an unusual feature in this species. Megagametophyte development is monosporic or (occasionally) bisporic. Megaspore tetrads are linear or T-shaped. Double dyads and tetrads are frequently observed.-Maintainance of subfamily status for Cordioideae is supported. [ABSTRACT FROM AUTHOR]

The two characters used by Burtt (1974) to segregate the genus Schizoboea from Didymocarpus, viz. 'terminal inflorescence' and 'fruit splitting into 4 valves', have been studied in detail: (a) The 'terminal inflorescence' represents a bracteate florescence (sensu Troll), that is an open thyrse, peculiar because of its only two extremely condensed internodes ('basic internode' + 1 following internode). Correspondingly, there are only two pairs of bracts from which the lower one only is capable to develop axillary partial florescences, i.e. pair-flowered cymes. Thus, the number of cymes is restricted to 2. Because of the condensed internodes, the inconspicuous bracts, and the densely aggregated flowers the two cymes simulate a unitary, terminal structure. By sympodial (± asymmetrically dichasial) linkage of shoot units, composed of an extended internode, a foliage leaf pair (from the axils of which the consecutive units arise) and the florescence, Schizoboea forms (polytelic) anthocladial shoot systems like some genera of the tribe Klugieae (incl. Loxonieae). (b) The fruit dehisces first loculicidally, then each valve splits into three portions (lateral rib and 2 semivalves). Moreover, the 4 placentae become isolated, thus the old fruit comprises 10 elements forming a loose fascicle.-The segregation of Schizoboea from Didymocarpus is supported. Whether the affinity is closer to Saintpaulia (as suspected by Burtt) ot to Didymocarpus, remains undecided: In regard to its shoot and inflorescence organization a morphological derivation is possible from both genera. [ABSTRACT FROM AUTHOR]

The embryology of Heliotropium scabrum and H. strigosum has been studied. The development of the anthers follows the dicotyledonous type, the tapetal cells become binucleate. The pollen grains are shed at the two-celled stage. Megaspore tetrads are linear and the development of the megagametophyte corresponds with the Polygonum type. The endosperm is cellular. The embryo development follows the Onagrad Type, i.e. the Capsella variation in H. scabrum and the Nicotiana variation of the Solanad Type in H. strigosum. The pericarp is differentiated into a one-layered epicarp with bulbous-based, unicellular hair, a 5-6-layered chlorenchymatous mesocarp and a 6-7-layered endocarp. The seed coat consists only of the thickened portions of the epidermis. [ABSTRACT FROM AUTHOR]

The shoot organization and inflorescence structure of Epithema is analyzed. On the main axis micro- and macrocotyledon (the latter falling off early) are followed by a ± long epicotyl, then a large, solitary leaf (B) and above this a dimerous leaf whorl (B, B). The last internode of the main axis is the 'basic internode' of the 'main florescence' ( Troll). Peculiarly enough, the latter includes only one 'partial florescence' which is embraced by its subtending bract (B) and represents a capitulum-like, congenital, pair-flowered cincinnus. Paracladia arise from the axils of B to B (sometimes also from the macrocotyledon); they are either reduced to their co-florescence (with the same structure as the main florescence), or carry further shoots resp. co-florescences from the axils of a dimerous leaf whorl.- Epithema can be interpreted as anisophyllous.-From flower morphology and ontogenesis a number of new differential characters are revealed. Together with shoot and inflorescence characters their systematic and possible functional significance is discussed. [ABSTRACT FROM AUTHOR]