316 BROOKLYN BOTANIC GARDEN MEMOIRS 
tree, the pistillate plant of this dioecious species has been proved to 
mature its stigmas synchronously with the shedding of pollen from 
the staminate trees. The yearly variations from the above dates 
vary according to environal—mainly heat—stimuli. Thus in 1912, 
after a cold February and early March, succeeding favorable days 
caused complete pollen dispersal on the 27th and in part on the 28th. 
During the precocious springtime of 1913, the flowering occurred 
suddenly and uniformly on the morning of March 18, while in the suc- 
ceeding year like expansion took place on March 31. The Carolina 
poplar (Populus deltoides) is like the last species specially abundant 
in the staminate trees, rare in the pistillate ones. Its average bloom- 
ing period is April 16. In 1913 its behavior was arresting in the sud- 
den and exact procedure shown. Here, these trees under similar 
environment lengthened their catkins fully and started to disperse 
abundant pollen on March 24, between 9 and 10 A.M. of a bright 
warm day. The young catkins were almost emptied by 5 P.M., 
only a few of the smaller terminal flowers still retaining a quantity. 
By next day, scant remnants could alone be secured. But on that 
day four trees which grew on wind-swept and shaded street corners 
were found only beginning to dehisce. 
In 1914, owing to prolonged cool periods and warmer ones alter- 
nating, blooming occurred on April 6. Many catkins matured only 
on the 7th. During the present year, the action and reaction of 
environal energy and of organismal tissue have been most suggestive. 
For stimulated by the bright warm suns of March 31 and April 1 
‘some catkins lengthened gradually during these and succeeding days, 
and began to discharge pollen extensively on April 4. But rather 
low temperatures on that day and those succeeding, accompanied 
often by rain, prolonged reaction fitfully until the roth of the month. 
So we learn from such statistics, that have frequently been verified 
for the above, as well as for other species, that if a sufficient environal 
stimulus act quickly and continuously, an extensive synchronous 
blossoming may ensue, that is completed within a few hours each year. 
On the other hand, if temperature units be more gradually expended, 
and specially if such be combined with wetting conditions that prevent 
establishment of tissue tension in anthers, pollen discharge may be 
prolonged over a considerable period. 
The alder (Alnus incana) that averagely lengthens and opens its 
catkins on March 24, and that shows crimson papillose stigmatic 
surfaces in exactly synchronous manner, was in like state on the 25th, 
but in 1913, March 12 was the date. Pollen dispersal is usually com- 
pletely effected in three or at most four days, this lengthened period 
being due to differences in position and so in time maturation of the 
catkins on each twig. 
