710 SUMMARY OK CURRENT RESEARCHES RELATING TO 



Cytology of Apospory.* — L. Digby lms studied the aposporal de- 

 velopment of prothallia in Nephrodium pseudo-mas var. cristata, which 

 occurs when fronds are pegged down in moist earth. The growth is 



rapid and prolific ; fronds treated during spring and summer showed 

 prothalli with embryos in three weeks. The young plants showed the 

 same character, which seems constant, as no case of sporangium or sorus 

 has appeared on the leaves. The prothallial growth arises from the 

 edge, or sometimes the surface, of the frond, as an outgrowth from the 

 marginal cells and those lying directly beneath the margin of the leaf. 

 The majority have the typical shape except that the cushion is not well- 

 developed ; antheridia are frequent, but archegonia were never seen. 

 The prothalli generally bear an embryo, in various stages of growth, 

 situated in the position normally occupied by the cushion. It arises as 

 a direct vegetative outgrowth from the prothallus, and when very young 

 consists of a rounded mass of cells, in which the apical cells of the 

 cotyledon, stem, and root are clearly recognisable. The longitudinal sec- 

 tion of an older plant is of a normal type, except for the absence of a 

 foot. The nuclear divisions were studied both in the prothallus and 

 embryo, and the number of chromosomes was found to be approximately 

 the same in the two cases (about 50), thus proving that there is no 

 reduction during the transition of the sporophyte to the gametophyte 

 generation. There was no clear evidence of the nuclear migration which 

 is so characteristic a feature of the apogamous prothallia of N. pseudo- 

 mas var. polydactyla. 



Structure and Development. 

 Vegetative. 



Axillary Scales of Aquatic Monocotyledons.! — R. J. Harvey 

 Gibson compares the ligule of Selaginella with the axillary scales which 

 occur in many members of the series Helobiere of Monocotyledons. 

 He suggests their phylogenetic importance from the point of view that 

 aquatic Monocotyledons may be regarded as modern representatives of 

 the more primitive Angiosperms, and that these in turn may have been 

 genetically related to some ancestral form allied to Iscetes. The scales 

 were examined in 17 species, representing 13 genera belonging to 

 6 natural orders of Helobieee. 



Reproductive. 



Morphological Study of Ulmus americanus.J — C. H. Shattuck has 

 studied the development of the spores, the process of fertilisation, and 

 the embryology in this species, with a view to a comparison with allied 

 members of the ArchichlamydeEe. He finds that the microsporangia are 

 in the mother-cell stage early in February ; they probably pass the winter 

 in this stage, forming tetrads at the first breaking of winter weather. 

 The tapetum is formed from the peripheral layer of sporogenous tissue. 

 The pollen-grains leave the tetrad stage in the middle of March, and 

 generally show tube and generative nuclei at this time. The male cells 

 appear by March 23, and the dehiscence of the anther occurs from 



* Proc.Eoy. Soc, series B, lxxvi.(1905) pp. 463-7. 



t Journ. Linn. Soc. (Bot.) xxxvii. (1905) pp. 228-37 (2 pis.). 



X Bot. Gazette, xl. (1905) pp. 209-222 (3 pis.). 



