244 LEAVES 



or furnish means for the activity of the protoplasm. So 

 we see why freezing weather and long droughts have prac- 

 tically the same effect on plants ; they both affect the water 

 supply. Cold apparently does not affect plants directly 

 in the manner in which it affects us directly. Indirectly, 

 however, through stopping the water supply or by freezing 

 the water already inside of plants, it has an even greater 

 effect upon them than it has upon us. 



Under these circumstances we can see why the loss of 

 the leaves is so great a means of protection to the plant 

 as a whole. If the wide, green leaves were present in 

 winter, there would be great loss of water by transpiration, 

 especially on dry days when the temperature is above the 

 freezing point. The roots in the frozen soil would be 

 entirely unable to make good this loss, and the death of 

 all the aerial parts would result. 



The following quotation sums up this matter : — 



" The shedding of leaves at the inception of a cool or 

 dry period is of inestimable advantage, especially in trees 

 with dehcate leaves, because of the enormously reduced 

 transpiration thus resulting. The leafless tree is one of 

 the most perfectly protected of plant structures, since the 

 impervious bud scales and bark cover all exposed portions." 

 (Cowles's Ecology.) 



Of course when we speak of an advantage to the plant 

 in losing its leaves, we are assuming that it has enough 

 food stored up to nourish it until new leaves become active 

 in the next growing season. The advantage is even more 

 evident for plants which shed their leaves at the approach 

 of a dry season than for those which shed them at the 

 approach of winter. 



Probably our evergreens have occurred to you in con- 



