314 BROOKLYN BOTANIC GARDEN MEMOIRS 
Plant variation as due to varying environal stimuli is a phenomenon 
witnessed everywhere around us. The difference in size and color 
between similar plants growing in shade and sunshine; the difference 
in growth and habit between plants exposed to moist rich soil and to 
light dry sand; the difference in time of leafing, blooming, and fruiting 
between plants situated at lower and higher levels, are facts that are 
familiar to all. But the fundamental causes of such differences, as 
well as the important conclusions to be drawn, have hitherto been too 
much overlooked. Even the records of leafing, the blooming and 
fruiting of flowering plants, the shedding of spores by pteridophytic 
and bryophytic species, or the conjugation period of algoid and fungoid 
types have often been given in most haphazard, or totally misleading, 
manner in many of our local floras and manuals. 
We desire, therefore, to inquire how far such great seasonal con- 
ditions as the above can be reduced to exact limits, and if possible to 
ascertain what fundamental principles underlie their expression. The 
writer selects first the blooming period of higher plants as a phenome- 
non that all can witness and verify to greater or less degree in daily 
life. Given that some one locality is chosen where a certain number of 
individuals of a species are exposed to as exactly like environal con- 
ditions as possible, it may then be asked how nearly synchronous may 
the blooming periods be amongst these, and how correctly can we 
define these for any region. In illustration, the following may be 
cited from amongst many others that the writer has watched 2 
Neglecting the wayward skunk-cabbage—that nevertheless can be 
reduced to system—the first plant to bloom each season is the silver 
maple. This year (1917) hundreds of trees opened many flowers 
synchronously on March 11, instead of on the 13th, as is averagely 
the case. -Furthermore, the opening took place about nine to eleven 
A.M. Favored by bright suns the expansion continued upward along 
the branches, as is averagely the case, for a period of nine days, and 
by this time the earliest flowers were beginning to push out their 
green fruits. If we compare now the same trees for previous years 
it may be said that during 1912, and as a result of continued snows 
and frosts, the unfolding occurred with equal abundance and exactness 
on March 17. In 1913 a remarkable record was made. The weeks 
of fall weather during 1912 were balmy and mild, and even at times 
warm. Asa result many heat units over the average were absorbed 
by the trees and caused precocious though unobserved preparation for 
spring unfolding in 1913. And here we would emphasize again, con- 
trary to views previously expressed by many, that record must be 
kept of environal conditions continuously throughout years, if true 
* The results recorded are given for West Philadelphia unless otherwise stated. 
