The External Features of Stems 



117 



perate climates. The buds of most temperate perennials are 

 covered with specialized scale leaves. Frequently the outer or the 

 exposed parts of scales die with the approach of winter. Not 

 infrequently the scales are further covered with matted hairs and 

 secretions of wax and resin. These all tend to make the bud 

 coverings impervious to water. 

 By these coverings the tender 

 growing parts are protected 

 from excessive loss of water 

 during the winter and during 

 the still more critical stage in 

 early spring when the buds are 

 opening. Bud scales do not 

 protect the growing point of 

 the stem from low tempera- 

 tures. During zero weather all 

 the tissues of buds and twigs 

 are frozen soHd. 



We are likely to think of 

 buds as being formed at about 

 the time when the leaves fall 

 from the trees. A good ob- 

 server, however, will have 

 noted that the buds begin to 

 develop when the leaves un- 

 fold in spring, and that they 

 grow all summer long. Be- 

 cause of the prominence of 

 the leaves, the buds are ob- 

 scured somewhat during the 

 summer months and become ^^^ ^^ ^^.^^ ^^ ^^.^^^ ^^^^ ^^^^i^^^^ ^s), 



conspicuous only after the and tree-of-heaven {Ailanthus) (C). The 



leaves have fallen from the 'T'\'^^^'^^'\''T''''''^,\VlZi''Tl 



buds; c IS a leaf scar, a a bundle scar, e, a 

 trees. lenticel, / a terminal bud scar, and g a tendril. 



