Volume 96, Issue 4
October 1986, pages 247-334
pp 247-271 October 1986
A survey of literature shows that somatic embryogenesissensu stricto has been achieved in only 102 species, subsequent plantlet formation in 51 of these species and eventual propagation in still fewer of them. The contrast between zygotic and somatic embryogenesis is rather marked. The potential for somatic embryogenesis is genotype-specific. Ultrastructural, histological and biochemical studies are limited. Published evidence shows that auxins affect both transcriptional and translational events involved in the induction of somatic embryogenesis; nonetheless, the primary action of auxin is not known. Growth inhibitors occurring in developing seeds play a significant role in somatic embryogenesis. Employing histologically simpler tissue systems such as nucellus and endosperm as primary explants is advocated. Some limitations in the existing studies and certain prospects are identified.
pp 273-279 October 1986
The quality and quantity of carbon and nitrogen substrates of growth media variously modified the mycelial growth and pathogenicity ofRhizoctonia solani. There was no correlation between rates of mycelial growth in different substrates and pathogenicity to cowpea seedlings. Disease incidence increased with the increase of carbon and nitrogen concentrations in media in which the fungal inocula was raised. Pathogenicity was maximum when the inocula was raised in media containing glucose and ammonium sulphate as carbon and nitrogen sources, respectively.
Disease control by 3 fungitoxicants carbendazim (Bavistin, 50% WP), quintozene (Brassicol, 75% WP) and methoxy ethyl mercury chloride (Emisan, 6% Hg) used as seed treatment in cowpea was variable whenR. solani inocula raised in different C and N amended media was used for soil infestations. Disease control by fungitoxicants was reduced when inocula were raised in media having higher concentrations of carbon and nitrogen. Inocula grown in media containing sucrose and ammonium sulphate decreased disease control by fungitoxicants. Disease control by carbendazim was least affected by inocula grown in different substrates compared to methoxy ethyl mercury chloride and quintozene.
pp 281-288 October 1986
The morphology and vasculature of the floral disc have been studied in 30 species of Lamiaceae to discuss its phylogeny. In Lamiaceae the disc receives vascular supply mostly from the gynoecial bundles which indicates its association with the gynoecium. Further, the evolution of both the external form and vasculature of the floral disc progressed independently. On a comparative basis the disc in prostantheroideae and scutellarioideae can be looked upon as most primitive, whilst in ocimoideae as highly evolved.
pp 289-301 October 1986
An attempt was made to verify the differential ecological preferences of calcareous and non-calcareous Myxomycetes from published records of Indian Myxomycetes. A definite preponderance of calcareous species on dead leaves and of noncalcareous species on dead wood and bark was noted. Myxomycetes in general occurred in large numbers at altitudes above 500 m; a temperature range between 15–20°C and a low (0–250 mm/month) or medium (250–500 mm) rainfall favoured their growth and sporulation. The calcareous species were more tolerant of the tropical climate than the noncalcareous ones. A limited analysis of the pH level and calcium content of the substrates from our collections suggested that the calcareous species preferred dead leaves for their calcium content, but pH of the substrate had no role in this specificity.
pp 303-309 October 1986
Cytological effects of different concentrations of 3 organophosphorus insecticides viz malathion, parathion-methyl and quinalphos were studied onAllium cepa L. root meristems. Root meristems were exposed to the test solutions for 1 h followed by different recovery periods (0, 4, 12, 24 and 48 h) in Hoagland’s nutrient solution. Among the 3 insecticides tested, parathion-methyl is found to be the most effective clastogenic as well as turbagenic agent. Malathion induced wide range of clastogenic effects whereas quinalphos is shown to be weak clasto- and turbagenic agent.
pp 311-314 October 1986
The anther development conforms to the dicotyledonous type. The tapetal cells are binucleate, glandular and dimorphic. The pollen tetrads are isobilateral (69%), tetrahedral (22%) and decussate (9%). The pollen grains are shed at 2-celled stage. The development of embryo sac is of the Polygonum type. The endosperm isab initio cellular and its development conforms to ‘Stachys type’. The embryo development follows Mentha variation of Onagrad type. The seed coat is 1–3 layered. The pericarp consists of 3 zones. The outer epidermis is non-mucilaginous. The seed is non-endospermic.
pp 315-320 October 1986
124 accessions belonging to 9 species of the genusMorus from diverse geographical sources have been studied for their sex expression. Studies cover 6 observations for 3 years including different seasons. Of the 124 accessions, 75 are dioecious, 44 are monoecious and 5 are non-flowering. Among dioecious accessions, 17 (13·7%) bear exclusively male flowers, 58 (46·7%) bear exclusively female flowers. Various combination of male and female flowers both in frequency and position have been observed among monoecious accessions. Several variations right from exclusively unisexual type to hermophrodite flowers are reported.
pp 321-326 October 1986
Cassia obtusifolia andCassia tora are distinct in several important phytochemical characters. Obtusin, obtusifolin and stigmasterol are confined only toCassia obtusifolia and chrysoobtusin toCassia tora. They also differ in their amino acid constituents. Cyotine y-hydroxyarginine and aspartic acid are present inCassia tora but absent inCassia obtusifolia. Hystidine, which is present inCassia obtusifolia is absent inCassia tora. Also there was no natural hybridization betweenCassia obtusifolia andCassia tora and thus showing complete genetical segregation. This supports their treatment as two distinct species. The presence of 3 additional secondary constituents, stigmasterol, obtusin and obtusifolin inCassia obtusifolia suggest thatCassia tora was derived fromCassia obtusifolia.
pp 327-332 October 1986
Observations on the vascular anatomy of the flower inTristellateia australis A Rich andStigmaphyllon ciliatum A Juss of the Malpighiaceae andSisyndite spartea E Mey andGuaicacum officinale Linn. of Zygophyllaceae are presented. These studies record varied forces of cohesion and adhesion between vascular traces to different floral whorls. The sepals and petals are unequal in size and a little oblique in some cases. Obdiplostemony is of less prominence and a disc is absent. There is a weaker cohesion of carpels, evidenced both; morphologically as well as anatomically. Placentation is axile. The vascular anatomical characters of the flower appear to be distinctive and exhibit a lower level of specialization as compared to the other Geraniales.
pp 333-334 October 1986