TYPES AND KINDS OF STEMS 55 



spaces. The effect of freezing then is to draw water from the 

 cells, i. e., it is a drying effect. If the buds had no protection 

 on the outside, the ice would gradually vaporize and escape. 

 The bud coverings, however, prevent excessive loss of water, and 

 when warmer weather comes the ice crystals in the intercellular 

 spaces melt and the water is drawn again into the protoplasm of 

 the cells by osmosis (paragraph 365). Bud coverings probably 

 protect the young growing plant from mechanical injury also. 

 For the study of buds see Chapter IX. 



GROWTH OF STEMS. 



90. Definite and indefinite growth. In woody stems, 

 shrubs and trees, there are two types of growth in length of the 

 new shoots each year, definite growth, or determinate growth, and 

 indefinite growth, or indeterminate growth. In the larger 

 number of trees and shrubs of the North Temperate region the 

 growth is definite. It is usually completed by the middle of 

 July. A terminal bud is formed from which the following 

 season the shoot continues its growth In some of these buds 

 all the leaves of this shoot for the coming season are already 

 formed in miniature in the bud and are covered and protected by 

 the outer dull colored scales. During the growth of the shoot the 

 next season these leaves mature and unfold as the shoot elongates, 

 and then a new terminal bud is formed. In other cases not only 

 do the young leaves already formed in the bud expand, but new 

 leaves are formed as the shoot elongates. In indefinite growth, 

 however, growth in length of the shoot continues until late in the 

 summer or autumn, and the terminal bud as well as the terminal 

 portion of the twig dies. One of the lateral buds then acts as 

 the terminal bud to continue the growth the following season. 

 In the spice bush a considerable portion of the dead terminal 

 shoot remains and the following year the new growth comes from 

 the living lateral buds some distance back from the tip. In 

 the elm the terminal portion of the shoot which dies is small, 

 falls away, and the latest lateral bud to be formed appears to 



