in Plant Cytology. 199 



evolution consist ? If in passing from the simple to the com- 

 plex plants no girat variet}- of new primarj' 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 chemistrj^ 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 Cytology. — 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 suggestiv'e 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 



