118 AGRONOMY 



and the stems do not form strong buds at the tip. In these 

 the buds and stems are usually killed back several inches 

 annually. Flower buds that are formed in autumn are often 

 killed by the cold, especially by a cold interval in late spring 

 after they have started into growth. Flowers, of course, are 

 sensitive to cold and may fail to set fruit even if the temper- 

 ature does not fall to the freezing point. In severe winters 

 the trunks of trees are often split open by the cold. Another 

 effect of the cold is seen in the improvement in the flavor of 

 certain vegetables such as salsify and parsnips. 



How plants avoid the effects of cold. Most perennial plants 

 have devised various ways of protecting their more delicate 

 parts from the cold. A large number have developed the 

 geophilous, or subterranean, habit, and at the approach of cold 

 weather the parts above ground die and the life of the plant 

 retreats to the underground parts. Examples are seen in the 

 species that produce bulbs, conns, tubers, rhizomes, and sim- 

 ilar structures. The same arrangement also protects from 

 drought. Bulbous plants are always plentiful in dry regions. 

 Plants above ground have other means of protection. The 

 trees protect the living cambium by a thick and nearly water- 

 proof bark, and their buds are protected by scales, hairs, and 

 varnish. Most of the broad-leaved trees drop their leaves to 

 avoid transpiration, but the pines and their allies with needle- 

 shaped leaves that do not transpire much are not obliged to do 

 so. The twigs and stems of many plants have a dense coating 

 of scales, epidermal hairs, or wax, as an additional protection. 

 How effective epidermis and bark are in retaining moisture 

 in the plant may be seen by comparing the behavior of a 

 peeled apple or potato with that of one in its natural state. 

 Herbs that retain their leaves adopt the rosette habit, and thus 

 their leaves, close to the earth, are protected all winter by the 

 dead vegetation and the snow. The majority of these devices, 

 it may be noted, are not so much protections from the cold 



