938 



ECOLOGY 



because of locally favorable 

 temperatures, buds germinate 

 soonest on sunny slopes, and 

 willows on the tundra come 

 into flower while their roots 

 are still in frozen soil. The 

 resting buds of herbaceous 

 plants, represented by bulbs 

 and bulbils (the latter de- 

 veloping into hulblings, figs. 

 1232, 1233), and by the buds 

 of tubers (fig. 1037), of rhi- 

 zomes, and of multicipital 

 herbs, germinate under con- 

 ditions similar to those that 

 incite activity in the resting 

 buds of trees and shrubs. 



Climate and bud development. — 

 As a rule, trees and shrubs with 

 large buds (as the poplars, willows, 

 and alders, fig. 1234) develop vig- 

 orous shoots early in spring, while 

 species with small buds (as the ca- 

 talpa and the honey locust) develop 

 much later. Such differences seem 

 to follow from the fact that in the 

 former the embryonic shoots are 

 much the more advanced while still within the resting bud. Many of the large- 

 budded forms which thus develop at the inception of spring are northern species, 

 and such habits seem very advantageous for far northern plants, owing to the short- 

 ness of the vegetative season. On the other hand, where the vegetative season is 

 long, small buds seem advantageous, owing to their exemption from the develop- 

 ment of extensive protective structures. Some large-budded trees, such as the 

 hickory, are both late in germinating and relatively southern in distribution. 



Fig, 1234. — -A branch of the European alder 

 {Alnus glutinosa) in its winter aspect ; j, the buds 

 of staniinate inflorescences ; /», the buds of pistil- 

 late inflorescences ; /, fruit cones of the preceding 

 year ; /, leaf buds. 



