130 Moore: The study of winter buds 



show a variable development. 



Ulmus 



catkins of Almis were noticeably larger in January. In some 

 cases the catkins of 5^//V and P^?////;/^ had pushed aside their scaly 

 coverings as early as December, but such p^'ecocious growth in 

 these two genera is confined to the flower buds of saplings and of 

 immature growths. Favorable situations and exposure to warm 

 sunshine are apparently factors which influence such premature 

 development. 



Sendtner (1851) observed that different parts of a plant show 

 a different attitude toward the varied influences and growth stimu- 

 lations affecting them during the winter months. 



According to Schimper (1903), it has been proved experimen- 

 tally that the flower buds, or reproductive organs, possess a lower 

 optimum temperature for growth than is the case with leaf buds, 

 or vegetative organs. This principle is apparent in nature, since, 

 in each species observed during the winter of 1905—6, the true leaf 

 bud is in all respects less active than the flower bud. 



Wiegand (1905) mentions the fact that flower buds do not in- 

 crease in size until late spring. Similarly, the leaf buds of the 

 trees and shrubs studied in this investigation show practically no 

 increase in size during the winter rest-period. At least their nor- 

 mal condition of apparent rest is not disturbed in so far as their ex- 

 ternal appearance is concerned. 



The curves of growth (figures A-J^ indicate a slight alternating 

 increase and decrease during the winter, a gradual increase during 

 March and a more rapid advance in April. The fluctuations of the 

 curve during the winter months are a result of difficulties encoun- 

 tered in measuring the buds. The outer scales often dry out and 

 many either loosen or fall away. This is clearly the case in Hicoria, 

 Picea, and Alniis. The quantity and consistency of scale varnish 

 varies also. But in spite of these difficulties a gradual continuous 

 growth, if present, could not fail to be observed and recorded in a 

 series of measurements which are made at regular and frequent in- 

 tervals during the winter and spring. The curves of growth are 

 therefore of value in illustrating the time and rapidity of swelling, 

 as well as the variations which are exhibited by the different gen- 

 era and species. 



The time at which the different plants under investigation 



