in Plant Cytology. 203 
of the morphological but equally of the physiological specific 
characters of plants. In my study of the great p.ysiological 
group which we commonly speak of as “ sensitive piants,” I 
have been impressed by the evident specific physiological 
relation of the tissues to environmental conditions. In cold 
countries such plants can scarcely be said to exist, except in 
the person of the Wood Sorrel, in milder regions they begin 
to attract some attention, in sub-tropical countries they are 
pretty frequent, and in tropical regions they often give a 
character to many landscapes. But the increase in num- 
ber of sensitive species toward the Tropics is correlated with 
increased sensitivity, so that from the Wood Sorrel to the Sen- 
sitive Plant we can arrange a graded series which show on 
stimulation a shorter latent period, increasing capacity for 
propagation of stimulus, a quickened period of contraction, 
as well as reduced neutral period, and period of re-expan- 
sion. 
Bonnier’s beautiful investigations on lowland and alpine 
plants should furnish a model for many similar studies in the 
future. The modifications he traces in epidermal cuticulariza- 
tion, in chlorophylloid cells, in tracheidal tissue and other 
bundle elements, demonstrate the true morphological origins 
of our Alpine Flora. Such considerations inevitably lead us 
to inquire—What isa species? Instead of attempting a direct 
answer allow me, in a few lines, to speak of what I have 
ventured to call ‘“‘ taxonomic cytology.”’ 
(f) Taxonomic CytoLocy.—Even if one should speak with 
bated breath of things taxonomic, before a Society for Plant 
Morphology and Physiology, at the risk of being consid- 
ered a law-breaker, I will attempt to slip in the greater adjec- 
tival subject, under cover of the lesser substantive plea. 
Urgency seems to furnish the apology. During the past 
dozen years or thereby, as questions of heredity, transmission 
of character, and validity of species distinction have been 
