in Plant Cytology. 199 
evolution consist? If in passing from the simple to the com- 
plex plants no great variety of new primary constituents is 
observed, but rather an advantageous placing of those already 
existing to suit environmental conditions, evolution might be 
supposed to consist mainly in an increasing distributional 
adaptation of cell substances, some of which may at times be 
well developed, while others may remain latent, though the 
complex machinery in the latter case would be continued, 
ready to start the formation of temporarily undeveloped prod- 
ucts when appropriate external stimuli are applied. 
An important inquiry of the future then should be to ascer- 
tain minutely what cell substances, if any, are peculiar to the 
higher plants, to take accurate note of the occurrence, or the 
appearance and disappearance of elaborated products in related 
species, and to determine whether by altered environment 
products that seem for a time lost in the chemistry of the cell, 
may not reappear under altered sets or strengths of stimuli. 
We must therefore recognize, as a line of cytological 
inquiry akin to the last, but somewhat different in its method, 
my next topic, viz: 
(d) EXPERIMENTAL CytToLocy.—If plants can change under 
altered environmental conditions, such changes must first 
occur in cells or cell groups. By experimental methods often 
of a simple kind, wonderful insight has already been got into 
cytological adaptability to environmental stimuli. Without 
lingering over the old experiments on the thickening and 
strengthening of tendril tissues, when these successfully wind 
around other bodies, and their atrophy when the latter are 
wanting, we have recently got many suggestive thoughts from 
the writings of Bonnier, Henslow, Lazniewski, Goebel, Lothe- 
lier and quite recently of Teodoresco. Their studies on 
lowland and alpine plants, on inland and littoral plants, on 
xerophytic and hydrophytic plants, or on the response of 
plants to different light rays have opened up new possibilities 
