182 THE JOURNAL OF BOTANY 
niferous floras. So the climate and other causes, such as the 
relation of land to water and earth to sun or other light sources 
of the epoch, d tended to exclude the huge arborescent 
Equisetales and Lycopodiales, and Cordaitese became graduall 
extinct. Not only have physiological factors caused the crowding 
out of recessive, dwarf, and weakly forms, but t ey likewise 
necessitated special adaptations, as we have seen in the case of 
Calamites, for the support of the abnormal stems. 
But—and we must admit the anomaly—instead of progress- 
ing themselves, these very same plants, such as the Equisetales 
i odern t 
owth and development, or have become reduced. Compare 
h 
we see to what a great degree they have retrogressed, even though 
their later intermediate ancestors or divergent forms—EHquisetites, 
Lycopodites, &e.—may exhibit some approximation between the 
two forms, both in size and organization. 
Now Natural Selection does not necessarily imply the existence 
or essential importance of any influence of environment 
(Nature, 1908, July 16)—“we may regard it as feasible that 
brought into action by the former, the adaptations must be due 
mainly to external factors, which themselves in turn act upon the 
organism.. 
Doubtless these adaptations, aided by what De Vries terms 
parrieer or sudden appearances of slight deviations or forms 
