Observations on the Internal Structure of the Spermatozoid of Dictyota

The spermatozoid of Dictyota is shown to be structurally morelike a vegetative zoospore than was the case in Fucus. The mitochondria,golgi, overall shape of the nucleus, nuclear membrane, fat bodies,and miscellaneous vesicles are as in a zoospore; there is, however,a vestigial chromatophore without an eyespot and the ciliaryapparatus is specialized. In spite of the single flagellum thereare two basal bodies inside the cell, one of which is apparentlyvestigial, ending blindy in the cytoplasm; both the a similarinternal structure with nine fibres in the wall. A fibrous ‘root’,possibly homologous with the ‘proboscis’ of Fucus,arises near the outer side of the functional basal body; itis a band of about eight fibres passing through the cell withouttouching the nucleus but closely pressed to the inner facesof at least two mitochondria before ending in an unknown mannerat the cell surface. The internal structure of the flagellumis normal but the fact that the median strand is marked by arowspines has been used to demonstrate is a conclusive way thefacts of bilateral symmetry in the whole organ; Dictyota agreesexactly with Fucus and a previous error based on incompleteinformation has been corrected. The process of unwinding ofthe flagellum from the surface of the body after liberationfrom the antheridium is described and used to illustrate someunexpected properties of the surface membrane.     

Observations on the Fine Structure of the Zoospore of Oedogonium cardiacum with Special Reference to the Flagellar Apparatus

Parts of the flagellar apparatus both inside and outside thecell have been investigated in a preliminary way by sectionsand whole mounts. Zoospores from male plants of O. cardiacumpossess about 120 flagella, the bases of which are held togetherin a ring by means of a characteristically patterned fibrousband and some differently arranged more homogeneous material.Between each pair of bases a compound root passes backwardsinto the cell. Each root has two radially superposed components:the outer component consists of three fibres starting at thefibrous ring and passing backwards close to the cell surface;the inner component is shorter and stouter, extending backwardsfor an uncertain distance but penetrating forward below thefibrous ring, to end within the substance of the colourlessapical dome of the cell. The material of the inner componentof a root displays a regular crossbanding of alternate thinand thicker lines spaced at approximately 140A for each unitof pattern (i.e. two lines). The orientation of the free partsof the flagella with respect to the fibrous ring is such thattheir two central strands when seen in cross-section near thebase are obliquely vertical.     

Cytotaxonomic studies in the Adiantum caudatum complex of Africa and Asia. II. Autoploidy and alloploidy in African reprsentatives of A. incisum

A hybridization programme involving populations attributable to A. incisum Forsk. sens. lat. from several parts of Africa has shown that, while all those sampled are tetraploid (unlike the Indian equivalents which are predominantly diploid), they are not all genetically identical. One ecologically differentiated allotetraploid has been collected from Tanganyika (Mt. Kilimanjaro) and the pairing behaviour of its chromosomes analysed in a range of crosses involving oriental and African cytotypes. All the other African samples investigated appear to be of autoploid origin. This is the first demonstration of autoploid derivation in the genus Adiantum.     

Observations with the Electron Microscope on a Species of Saprolegnia

Electron micrographs are presented to show the morphology ofthe flagella in each of the two motile phases of Saprolegniaferax, and one visual light photograph of a stained cell ofthe second stage is added. The front flagellum of both phasesis a Flimmergeissel with hairs between 2µ and 3µlong arranged in two rows and each ending in a thin hair-point.The axis is covered by a wide transparent sheath made of somematerial which appears to liquefy after death. The hind flagellum,which is devoid of Flimmer, is covered by a similar sheath,though there are signs that this is flattened into a fin inthe hind flagellum of the second stage. Some very fine shorthairs 0?5µ long are interpreted as a possible internalframework to this fin. The axis of both flagella is fibrillar,but accurate numerical details have not yet been obtained. Theskins discarded from cysts have also been examined and shownto be covered with characteristic double-headed hooks, whichare strong enough to attach a cyst to passing objects.     

Further observations on Potamodiscus Gerloff =Pinaciophora Greeff, with special reference to Alaska and arctic Canada

Pinaciophora spiculata sp. nov. is described on the basis of two complete periplasts collected in arctic Canada at—l°C in 1973. One has been tested for silicon by means of X-ray microanalysis with strongly positive results. The species possesses dimorphic scales, the spicular scales and exceptionally small plate-scales being equally diagnostic. The circumstances under which the name has already appeared in the literature are explained. In addition, the known ranges of two other taxa are extended by broken periplasts recovered from other arctic or subarctic areas, notably P. denticulata Thomsen (plate scales only) formerly known from Peru and now from South Alaska (at Homer) while the type species of the genus ( Poturnodiscus kalbei Gerloff 1968= Pinaciophora fluivatilis Greeff 1875) is demonstrated both from South Alaska and from beneath sea ice in North Alaska, in both localities possibly introduced into the sea by freshwater drainage.     

Cytotaxonomic studies in the Adiantum caudatum complex of Africa and Asia

Study of meiosis in synthesized hybrids has permitted a genome analysis to be carried out with respect to the holotype of A. indicum Ghatak, 4x, originally found wild near Calcutta. The two differentiated diploids from which A. indicum , 4x, seems to have arisen are represented in the analysis by A. zollingeri from Ceylon and by two strains of an Indian diploid provisionally designated A. incisum sens. lat. 2x. Supplementary information excluding an autopolyploid origin for A. indicum is provided by hybrids between A. indicum 4x and an unrelated tetraploid, A. malesianum Ghatak. Ecological information is supplied for the material of A. zollingeri , indicating that it occupies a specialized habitat which might be found in India if search is made in the right kind of territory. A. incisum 2x is shown to be much more widespread and to be present in hill country, or occasionally in lowlands, from the Himalayas to South India inclusive. It contains a number of genetically determined biotypes differing slightly in morphology but behaving as members of one species when combined into hybrids. Further morphological information and a revised key for separating the specimens used in the investigation is provided in an Appendix.