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 

 2 1st 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 twejity 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 ruhrum) 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 a\'erage blooming date is 

 April 7, but this year, stimulated b>' 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 



