GROWTH AND WORK OP PLANTS 



shrubs form the buds towards the end of the growing season, the 

 winter is the resting period and this is the period through which 

 the delicate growing point of the shoot needs protection in the 

 bud. The covering of buds by the closely overlapping scales, 

 and by the wooly or hair-like covering of the inner scales of many 

 buds, or by hairs alone, as is the case in some buds, is generally 

 supposed to be a protection against freezing. This is not strictly 

 true, for ice is abundantly formed within the buds during very 





Fig. 51. 



Section of frozen bud of Populus dilitata showing ice from water drawn from the bud leaves 

 (from K. M. Wiegand). The white crescents are masses of ice between the bud scales. 



cold weather even in buds well covered with scales or hairs. It 

 is rather a protection against the loss of water from the delicate 

 tissues of the bud. This protection applies then to- buds in 

 climates where the resting season for vegetation is dry and hot as 

 well as in climates where the resting season is very cold. When 

 freezing takes place (in plant tissues a little below the freezing 

 point for water outside) the ice is rarely formed inside of the cells 

 in the protoplasm. The ice forms on the outside of the cells in 

 the intercellular spaces. As freezing continues water is drawn 

 from the cells and added to the ice crystals in the intercellular* 



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

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



