Volume 86, Issue 1
July 1977, pages 1-72
pp 1-13 July 1977
The unique pattern of angiosperm embroygeny provides few meaningful criteria for classification. The existing classifications are based solely on the early segmentation pattern of the proembryo. Analysis of angiosperm proembryo with regard to change in surface to volume ratio and segmentation of internal cells, provides significant criteria for a meaningful classification.
The outer surface of the zygote is exposed to an environment external to it, but the cells segmented by it become less and less exposed to the external environment and more and more to the internal environment. The segmentation of the first wholly internal cell or cells may be looked upon as the first important morphogenetic event that initiates an organizational change in the reaction system of the proembryo, as it results in the differentiation of two groups of cells which thereafter follow different developmental pathways.
In the proposed classification, (i) the number of cell tiers that comprise the proembryo at the time the first series of wholly internal cells are segmented, (ii) the relative location of the tiers with varying cell number, and (iii) the terminal or subterminal location of the tier in which the first internal cells are segmented, are employed as criteria to classify angiosperm embryos into groups, series and variations respectively. The different categories in each of the three criteria are separately numbered to characterise the embryo by an embryonic number.
pp 15-22 July 1977
In the selfed progeny of a diploid plant ofPennisetum typhoides (Burm) S and H, which was a translocation heterozygote and with chromosome number 2n=13+2 telocentrics, one triploid plant was obtained. In the open pollinated progeny of this triploid, one plant with chromosome numerical mosaicism, chromosome number varying from 2n=28 to 37 of which 23 to 33 normal chromosomes and 3 to 7 telocentrics, was obtained. In PMC meiosis higher associations of 5, 6, 7 or 8 normal chromosomes were observed. This plant was highly sterile. Of the five progeny plants that could be obtained on selfing and open pollination 4 plants showed chromosome numerical mosaicism and one plant had a constant chromosome number of 2n=26+4 telos. As this phenomenon of intraplant chromosome numerical variation can be transmitted from generation to generation it was considered to be genotypically controlled. It was further argued that gene combinations are responsible for the instability and not always associated with higher gene dosage and hence higher polyploidy as suggested by Gildenhuys and Brix in induced amphiploids of Pennisetum. The same factor that was responsible for the chromosome numerical mosaicism seemed to be responsible for the origin of the tetraploid from the triploid.
pp 23-31 July 1977
InMelampyrum pratense the anther is tetrasporangiate and anther wall consists of epidermis, fibrous endothecium, a transitory middle layer and glandular tapetum. The division of pollen mother cell is simultaneous. At shedding, the pollen grains are 2-celled, 3-colpate and spheroidal.
The gynoecium is superior and the ovary is bicarpellary, syncarpous with two tenuinucellate, unitegmic ovules in each locule.
A coenomegaspore with 1+3 arrangement of nuclei develops into a 7-nucleate embryo sac. The female gametophyte is tetrasporic and 7-nucleate.
Theab initio cellular endosperm is haustorial. The chalazal haustorium is large, binucleate and highly aggressive. The 8–16 nucleate micropylar haustorium is unicellular with 2–4 tubular processes, one of which is longer and aggressive.
pp 33-38 July 1977
The structural and chemical features of roots of 55 rice varieties were correlated with the degree of susceptibility to the root-knot nematode (Meloidogyne graminicola). Less roots, dense root hairs, highly sclerotised exodermis, narrow cortex and stele, few phloem points, low starch, protein and nitrogen, high lignification, high aspartic acid and alanine contents characterised roots of resistant rices.
pp 39-43 July 1977
In the laboratory studies,Agathis unicolorata (Shenefelt) larval parasite oviposits in the body cavity of the host larvaeP. operculella where parasite larva develops. The mature larva emerges from the host killing it in the process and spins a cocoon. The longevity of ovipositing females averaged 10 days (maximum 14). The mated parasite had on average ovipositional period of 8·5 days (maximum 12) and produced an average of 107·7 adult progeny of the both sexes. The sex-ratio male: female of their progeny averaged 2·1:1. The rate of multiplication (R0) was 34·56 times in mean generation time (T) 24·602. The intrinsic rate of increase (rm) ofA. unicolorata population under laboratory conditions was 0·144 per female per day.
pp 45-53 July 1977
The present study has indicated that sclereids constitute a generic character in the genusPlethiandra Hook. f. They are of varied types ranging from spheroidal to sclerocyst formation. It has been observed that a combination of their typological diversity and surface distributional pattern could be utilised as an aid in the identification of the taxon at the specific level.
pp 55-60 July 1977
The activity of iron-prophyrin enzymes, catalase and peroxidase in comparable young green, chlorotic and Fe-EDTA sprayed chlorotric leaves of ten plant taxa growing under field conditions was studied. Evidence is presented suggesting that during recovery from iron stress, iron requirement of catalase is met in preference to peroxidase. Iron chlorosis, though always accompanied by depressed catalase, was not always associated with a high peroxidase/catalase ratio.
pp 61-72 July 1977
The development of the foetal membranes in the Indian horse-shoe bat,Rhinolophus rouxi (Temminck) is studied. A diffuse chorio-vitelline placenta is present during the early gestation. This is abolished after the limb-bud stage due to the extension of the exocoelom between the splanchnopleure and the somatopleure. Finally the yolk-sac splanchnopleure lies near the placental disc as a collapsed bag with hypertrophied endodermal cells. The allantoic vesicle is large up to about mid pregnancy, but is lost in the latter half of pregnancy. An allantoic duct is present in the umbilical cord until full term. The definitive chorio-allantoic placenta is discoidal, mesometrial, labyrinthine, vasodichorial in some places and vasomonochorial in others. There is a deep cleft in the centre of the placental disc. Hence, in transverse sections the placenta appears to be partially divided into two discs.