10 Bulletin of the Umversity 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 
