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 century 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 hyphz of symbiotic 
fungi in the medio-cortex cells, in roots of orchidaceous, 
liliaceous, burmanniaceous and many dicotyledonous plants, 
suggests as pointed out by Groom, the presence of some 
chemotactically active product, for which the hyphez have an 
affinity. These are a few of the first gleanings ina great 
harvest of chemico-physiological generalizations that will 
doubtless be reaped in the century soon to begin. 
(c) EvoLutionary CytoLocy.—Since the formulation of the 
evolution hypothesis forty years 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 nauseam, 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 life 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 
