690 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The sterility of Cytisus Laburnum is due to the fact that the pollen 

 cannot germinate unless the stigma has suffered mechanical injury; 

 when this occurs, self-fertilisation is rendered possible. It is pro- 

 bable that many other Papilionaceas behave in a similar manner. In 

 Corydalis cava, the stigma must be injured before the pollen can ger- 

 minate, but the tube only penetrates a very short distance. In Secale 

 and Lilium hulhiferum, the pollen of the same flower may germinate, 

 but does not usually fertilise the ovules. Generally, in all cases of self- 

 pollination in the examined species, the growth of the pollen-tube ceased 

 before fertilisation, but there is no reason for supposing this to be the 

 result of lack of sexual affinity. Experiments on various substrata show 

 that pollen will germinate under conditions which will not support its 

 further growth : the tube starts growth, and may even penetrate the 

 conducting tissue for some distance, but unless on its own particular 

 substratum, it does not reach the gynoecium. From the negative results 

 of the experiments, there is no reason for supposing that pollen cannot 

 be nourished on an artificial substratum ; it can only be supposed that 

 up till the present time, the nutrient solutions have been lacking in 

 some substance which is necessary to bring the pollen-development to 

 perfection. This unknown substance is not the protoplasm itself, since 

 the pollen-tube and the cells of the conducting-tissue have unbroken 

 cell- walls. The substance must be soluble and diffusible, and must be 

 different in different plants. In closely related species and in different 

 forms of heterostyhc flowers, a quantitative difference in concentration 

 would be sufficient, but in self -sterile flowers there must be a qualibitive 

 difference. Whether the retardation of growth is due to identity 

 between some material in the pollen-tube and in the conducting-tissue, 

 or whether some difference in material promotes the growth of the 

 pollen-tube, cannot at present be decided. 



CRYPTOGAMS. 



Pteridophyta. 

 (By A. Gepp, M.A., F.L.S.) 



Philippine Ferns.* — H. Christ publishes a list of new or imperfectly 

 known ferns of the Philippine Islands, founded on collections made by 

 Loher, Copeland and Merrill. He enumerates 111 species, among which 

 are 27 new species with 3 new sub-species and 9 new varieties. Many 

 critical notes are inserted ; and the value of the secondary leaves in 

 separating the species of StenocMmna, and as indicating the Asplenoid 

 ■ ancestry of the genus, is pointed out. 



The same authorf gives a classified list of the Philippine species of 

 Dryopteris, not intended to be complete, but founded upon all available 

 material in the herbarium of the Bureau of Science at Manila, and the 

 collections of Copeland and Loher. The genus Dryopteris is limited in 

 the sense of Christensen's Index Filicum, that is, excluding Pleocnemia 

 -and Sagenia, and treating only Lastrea (including Phegopteris) and 



* Philippine Journ. Sci.. Manila, ii. (1907) pp. 153-88. 

 t Tom. cit., pp. 189-217. 



