MACFARLANE: SYNCHRONISM IN PLANT STRUCTURES 315 
results are to be secured as to the action of environmental agents. To 
attempt to start the record from such an artificial period as the first of 
any year is to set an arbitrary limit to the continuity of changes and 
activity in vegetation. 
The short-lived snow and slight frosts of late November started 
the apparently needful winter maturation of tissues, and_ this 
was followed by an almost continuous series of genial days until the 
third week of January. So on the morning of January 19 abundant 
first flowers expanded on all observed trees, but a cold wave on the 
21st split the flowering period in half, and only on March 2, with the 
advent of a bright day and warm sun did the opening again proceed 
until March 10. This striking result had not been paralleled through a 
previous period of at least thirty-five years. As a contrast, in 1914 ex- 
pansion occurred only on March 16, owing to the frosts and late tem- 
peratures occurring throughout February and on to March 15. In 
the neighborhood of Wayne, Pa., with an elevation of 475 feet, with 
greater exposure to cold winds and less influenced by the heat of a 
great city, the opening did not take place until the 22d of March. 
Records like the above that extend over more than twenty years would 
suggest that floral expansion is not a somewhat haphazard and irregular 
event, but is rather an exact reaction of an organism to definite and 
cumulated environal actions or stimuli. If such be true, we should 
expect it to extend probably throughout flowering plants as a group. 
Partial proof is subjoined. 
The red or swamp maple (Acer rubrum) each year succeeds the 
silver species in blooming at an average interval of twelve days. This 
year, eleven trees, observed in like locality, all opened on the morning 
of March 26, while the climax of blooming was reached on the 4th of 
April. - 
According to the valuable statistics secured by Dr. Mackay and 
his committee of observers, it may be instructive here to point out 
that the same species in Nova Scotia has expanded averagely on May 5, 
or 41 days later than in the Philadelphia region. 
The white poplar (Populus alba) is of exceptional interest from the 
standpoint of the present communication. Staminate catkins an- 
nually mature, and lengthen synchronously, amid like environment 
on a definite day, and the shedding of abundant pollen proceeds for 
one or at most two days. Thereafter the catkins soon shrivel and 
within a week have mostly fallen. The average blooming date is 
April 7, but this year, stimulated by the warmth of mid-March days 
the tassels suddenly lengthened on March 28. Pollen was completely 
shed by the 29th, and sidewalks over wide areas were covered with 
fallen tassels by the 2d of April. But though a comparatively rare 
