Volume 16, Issue 5
November 1942, pages 121-164
pp 121-140 November 1942
This paper is a detailed account of the structure and development of the endosperm and thevermiform appendage.
After fertilization some free endosperm nuclei are formed, and these are distributed in the upper two-thirds of the embryo-sac, with a strong accumulation at the micropylar end. The organization of cellular endosperm begins a little later, and in this only the nuclei in the micropylar end participate. The rest of the embryo-sac becomes zig-zag in its form and develops into a cœnocytic haustorial structure with a strikingly worm-like appearance. This is designated thevermiform appendage which was discovered by the writer. The antipodal cells are seen persisting at this stage and also later.
Thevermiform appendage shows two distinct phases in its growth and development; the first phase is characterized by the cœnocytic nature of theappendage with free endosperm nuclei, and the second by the formation of cross partitions followed later by cell formation to give rise to a secondary endosperm tissue. In mature seeds both theappendage and the endosperm tissue are completely used up by the embryo.
The nature and origin of thevermiform appendage are discussed in the paper.
pp 141-154 November 1942
The paper gives a brief account of the cytological studies on the Hepaticeae and indicates the bearing of these on the problem of the phylogeny of the Marchantiales. The data available have been analysed and grouped under the following four headings: the sex chromosomes, hybridization, polyploidy and gene mutations, and the morphology and numbers of chromosomes. The information regarding the chromosomal numbers has been tabulated and the probable basic numbers in different families have been indicated. From the table given on page 145 it will be seen that the basic number of chromosomes (gametophytic number,i.e., ra-number) for the majority of the genera of the Marchantiaces and the Jungermanniaceae seems to be 9, and for the genera of the Ricciacete it seems to be 8. In the light of this cytological observation the existing schemes of classification of the Marchantiales have been examined with a view to knowing how far the morphological data and the cytological data are correlated. If it be supposed that the basic complex of the ancestors of the Marchantiales called Pro-Marchantiales in this paper, had 8 chromosomes in their genom and changed to a 9 chromosomal condition later by fragmentation, then there is some justification for the progression hypothesis. On the contrary, if it be imagined that the Pro-Marchantialean complex consisted of 9 chromosomes originally and got reduced to 8, the reduction hypothesis may seem plausible.But when either of these ideas are pressed further and the number of chromosomes in different genera in the various schemes of classification given by Cavers, Kashyap, Verdoorn and Evans are considered, the verdict of cytology on either of these schemes is not unequivocal, as the main argument brought in the discussion for or against a theory is based on the difference of a single chromosome only; and it may well seem doubtful whether that alone can constitute sufficient proof for or against a scheme.
pp 155-164 November 1942
The development of microsporangium inPedalium murex Linn., is of the normal type. The cells of the primary sporogenous layer function directly as the pollen mother cells. The tapetum is multi-nucleate and exhibits nuclear fusion, prior to disintegration.
InSesamum andPedalium the embryo-sac development conforms to the normal type. Chalazal nutritive tissue is met with inPedaliuin, while it is absent inSesamum.
Endosperm is cellular. The occurrence of chalazal endosperm haustoria is reported in both the genera. No micropylar haustorium was observed. The chalazal haustorium is single celled and four nucleate inPedalium, while it is made up of two bi-nucleate cells isSesamum.
The diploid chromosome numbers ofPedalium murex andMartynia diandra have been determined for the first time to be sixteen and thirty-two respectively. In the case ofPedalium the number is confirmed from meiotic counts also which shown=8.