10 Bulletin of the University of Texas 



forester can usually determine the species of tree by the bark 

 characteristic alone. 



The function of the bark is to prevent loss of water and to 

 protect the delicate inner* living tissues from the entrance of 

 parasitic fungi and bacteria which would lead to the decay and 

 death of the tree. Injuries which break the continuity of the 

 bark are the most frequent causes of diseases of trees. The gnaw- 

 ing of the bark by horses is one of the serious menaces to street 

 shade trees, and they should always be protected against it. The 

 bark forms a very effective protective layer which, if uninjured, 

 usually suffices to keep most trees in a relatively healthy condi- 

 tion. It is, however, provided on young portions with openings 

 which are necessary to furnish a means for aerating the stem. 

 These openings are known as lenticels, and they furnish an un- 

 avoidable avenue for loss of water and for the entrance of fungi 

 and bacteria. 



A bud may be defined as an undeveloped shoot. The forma- 

 tion of buds takes place during the active growing season, which 

 in our latitude lasts until the middle or latter part of July. 

 After this time the tree continues to manufacture food and store 

 it up in the buds and other organs until September or October, 

 when a period known as the winter rest period begins. This 

 lasts until the following spring, when the buds expand into leafy 

 or floral shoots. This rhythmic periodicity in the life of the tree 

 is directly due to the change of the season from conditions favor- 

 able to growth to conditions unfavorable. 



The bud contains, in miniature form, the leaves or flowers which 

 will appear the next year. These structures are very small, yet 

 all the parts are present. The outer part consists of a series of 

 leathery, scale-like leaves which overlap each other and protect 

 the delicate inner parts from injury. It is a popular notion that 

 the enveloping bud scales serve as a protection against cold and 

 keep the inner parts from freezing during the cold winter. But 

 this is not the case. There are in plants no provisions for main- 

 taining a body temperature higher than that of the surrounding 

 air, and there is no cold so intense that it could not be endured 

 by many plants if this were the only unfavorable factor. The 

 bud scales serve primarily as a protection against loss of water, 

 for which purpose they are well fitted. The mucilaginous or 



