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 pliants 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 ■? 



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 (19 17) 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 19 12 were balmy and mild, and even at times 

 warm. As a 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 



2 The results recorded are given for West Philadelphia unless otherwise stated. 



