WINTER CONDITION OF SHOOTS AND BUDS 63 



sues.* It was once thought that in the freezing of plant tissue ice 

 was formed inside of the cells, and that the protoplasm was killed 

 by the cold. But this rarely occurs. The water freezes on the 

 outside of the cell wall, and additional water flows out from the 

 inside of the cell and continues to freeze there building up ice 

 crystals in the intercellular spaces (fig. 48). If the freezing con- 

 tinues long enough, so much water may be drawn from the proto- 

 plasm in the cell as to make it too dry and thus kill it. When the 

 buds freeze the ice crystals are formed in the intercellular spaces. 

 When the ice crystals thaw the water is slowly absorbed by the 

 protoplasm in the cells again and is unharmed. Were it not for 

 the bud scales and other means for bud protection, the water 

 from the thawing ice crystals would evaporate and the proto- 

 plasm would be killed. The effect of freezing on plant tissue is, 

 therefore, in most cases the same as that of excessive dryness. 



105. Characters of winter buds and shoots. Winter buds 

 and shoots possess certain marks and other features which are 

 characteristic of the different kinds, so that a careful student of 

 these characters is enabled to tell the different kinds of trees 

 and shrubs from the winter condition of the shoots and buds.f 

 Some of these characters are as follows: The surface, whether 

 smooth or rough, shiny or dull, the color, the form of the lenti- 

 cels. The lenticels are minute elevations composed of corky 

 tissue with a minute opening, which serves the purpose of an 

 interchange of air and other gases, between the tissues of the 

 shoots and the outside. The shape of the shoots is another 

 character, also the form and arrangement of the leaf scars, with 

 their markings, the form and other characters of the buds, etc. 

 The characters of the following shoots will serve as illustrations. 



106. Shoots of the horse chestnut. Terminal buds. The 

 terminal bud where well formed is larger than the lateral buds. 

 This, as in other similar cases, is evidence that this bud will con- 



* See "Some Studies Regarding the Biology of Buds and Twigs in 

 Winter," Bot. Gaz., 41, 373-423, 1906. 



t See "A Key to the Genera of Woody Plants in Winter," 3rd edition, 

 '.908, by Wiegand and Foxworthy. Andrus & Church, Ithaca, N. Y. 



