in Plant Cytology. 197 



due to the retention in the cells of the growing apex of some 

 special protoplasmic compound. 



But the close of this centuiy has given us some valuable 

 illustrations of chemical relations between living cells which a 

 few decades earlier would have been regarded as physiologi- 

 cal. The chemotactic relation of sperm cells in the mosses 

 and ferns to definite chemical substances excreted by the egg 

 apparatus opens up a wide avenue for research that will not be 

 confined to fertilization phenomena alone. The remarkable 

 constancy in position, of the main mass of hyphte of symbiotic 

 fungi in the medio-corte.x cells, in roots of orchidaceous, 

 hhaceous, burmanniaceous and many dicotyledonous plants, 

 suggests as pointed out by Groom, the presence of some 

 chemotactically active product, for which the hypha; have an 

 affinity. These are a few of the first gleanings in a great 

 harvest of chemico-physiological generalizations that will 

 doubtless be reaped in the century soon to begin. 



(c) EvOLUTiox.\RY CvTOLOGV. — Since the formulation of the 

 evolution hypothesis forty j'ears ago, much has been written 

 on the factors of organic evolution. Many of the observa- 

 tions have been direct and valuable contributions to cytologi- 

 cal literature. But while such inquiries as "the possibility of 

 characters being acquired," or "the hereditary transmis- 

 sion of acquired characters," or " the action of environment " 

 have been debated almost ad nausca/n, the inquiry has not 

 been followed out in most cases, as an exact line of cytologi- 

 cal investigation, the results of which would aid us in deter- 

 mining what are the characters latent or observable which every 

 cell or cell-group possesses. 



With his usual sagacity Darwin constantly insisted on the 

 recognition of latent structures and functions as important 

 factors in the hfe of organisms. Molecular details which may 

 be entirely hidden even to our aided view, or subtle functions 

 which definite molecular combinations may call forth, might 



