ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 449 



Development of Pollen in Zostera.* — 0. Rosenberg finds that in 

 quite young anther rudiments the archesporial cells are very elongated^ 

 lying obliquely to the anther wall and stretching from one wall to the 

 other. From both ends of the archesporial cells isodiametric tapetal 

 cells are cut off, which divide several times and are finally dissolved. 

 The inner cells continue to elongate and divide longitudinally to form 

 numerous long cells, the pollen-mother-cells, which pass through a 

 long resting period. Other cells divide transversely to form the sterile 

 cells of the archesporium, which become crushed by the pollen-mother- 

 cells and gradually disorganised. The nuclei which are found later 

 between the pollen-cells are derived mainly from these sterile cells, but 

 in part from the dissolved tapetal cells. A long period of development 

 is passed before the pollen-mother-cells form tetrads, at this period the 

 proportion between length and breadth is 60 : 1, and the number of the 

 chromosomes is reduced to six. The first spindle is often sickle- or S- 

 shaped ; the nuclear membrane persists to the time when the daughter 

 chromosomes have reached the poles, a phenomenon which recurs in the 

 nuclear divisions in the root-apex of the same plant. The spindle and 

 also the cell-plate stand obliquely to the long axis of the pnllen-mother- 

 cell ; the cell-plate becoming more and more parallel with the latter. 

 The second cell-division is also longitudinal, as might be expected from 

 the characteristic packet of four thread-like cells. 



Finally the author discusses previously described instances of sterile 

 cells in archesporia ; he suggests that herein may lie the explanation 

 of differences in form of the pollen-grains in one and the same anther- 

 chamber. 



Embryology of Zostera marina.f — The same author finds that the 

 origin and development of the embryo-sac follow the course typical 

 for most angiosperms. From the embryo-sac mother-cell is formed a 

 series of four cells the lowest of which becomes the embryo-sac. The 

 embryo lies usually near the micropyle, rarely near the middle of the 

 embryo-sac. It is borne as a remarkably large one-celled pear-shaped 

 suspensor which contains a very large nucleus. The nucleus increases 

 in size until it almost fills the cell ; its appearance suggests an active 

 nutritive function. In formation of endosperm the nuclei lie free in 

 the parietal cytoplasm. 



The author also discusses the structure of the root, especially the 

 epidermis which shows well the arrangement into long and short cells. 

 From the peculiar structure of the nucleus of the short cells, which re- 

 calls that of the nuclei of nutritive cells, the author concludes that these 

 «hort elements are passage cells, whereas owing to their richness in 

 tannin the long cells probably cannot subserve this function. 



Development of Embryo-sac and Embryo in Castalia and Nym- 

 phaBa.J — M. T. Cook has investigated Castalia odorata and Nymphsea 

 advena with a view to reaching some satisfactory conclusion on the 



• Meddel. fr. Stockholms Hogskola Bot. Inst., 1901, pp. 21 (9 figs.). See Bot. 

 Zeit., Ix. 2 (1902) pp. 132-3. 



t Op. tit; Nr. 211 (1901) pp. 24 (2 pla. and 6 text figs.). See Bot. Zeit., 1. c> 

 pp. 131-2. 



: Bull. Torr. Bot. Club, xxix. (1902) pp. 211-20 (2 pis. and 2 figs.). 



