76 DEVELOPMENT AND HEREDITY. 



and folded them together during the day-time, — 

 proof enough that the rhythm of the after-effect 

 movements is totally dependent upon the manner 

 of the alternation of illumination to which the 

 plants have been exposed. 



"Many of our trees and bushes lose their foli- 

 age in the autumn and form winter-buds which 

 do not unfold until spring, and this is evidently a 

 peculiarity of the plants which is originally due to 

 the climatic conditions of our latitude. If a twig 

 covered with winter-buds be cut off in the fall, 

 and the stem put in water and set in a hot-house, 

 the buds will not immediately open as one might 

 perhaps expect, but on the contrary months often 

 pass before the buds unfold. From this it follows 

 that the season of plants can only be considered 

 as a phenomenon which is directly dependent on 

 external conditions. These conditions once cer- 

 tainly determined the growing period of the plants, 

 but this period has gradually become through after- 

 effects and inheritance, more and more fixed in the 

 organism, until now it is not easily made to dis- 

 appear. This can, however, gradually occur under 

 the influence of changed climatic conditions. A 

 proof is furnished, for instance, by the circumstance 

 that our cherry has become an evergreen tree in 

 Ceylon." 



