72 CHARACTER OF BUDS 



They have, however, the same arrangement as in the mature 

 shoot of the summer time and you should observe for a few days 

 in the spring the opening of a variety of buds, noting how this 

 crowded arrangement of the organs of the bud gives place to 

 that of the mature shoot. The formation of buds possibly came 

 about owing to climatic changes. The earlier vegetation of the 

 earth was subject to a uniform tropical climate but the formation 

 of high mountain ranges and other factors caused cold currents 

 of air to sweep over the earth and also produced variations in the 

 humidity of the atmosphere. These factors resulted in producing 

 a season favorable for growth and one in which growth would 

 be stunted or checked. The latter condition induced many 

 changes in the plant, of which the bud is an important example. 

 The great majority of woody plants are characterized by these 

 two phases: a period of rapid growth up to about the middle 

 of July, during which time all the organs of the season as well as 

 the buds are formed, after which they continue to manufacture 

 food and store it up in the buds and other organs until September 

 or October; and a period of dormancy in which the plant is in a 

 resting condition until the spring. Such a method of growth is 

 termed definite and should be distinguished from the indefinite 

 growth of a few plants such as the raspberries, locusts, some 

 honeysuckles, etc., where the growth goes on until the fall frosts, 

 with the result that the more recently formed, delicate parts are 

 killed off each year. But even in these cases we have essentially 

 the same rhythm of growth as in the first case because the -older 

 portions of the shoot have perfected their tissues and developed 

 their buds and so prepared for the dormant period. 



Whatever may be the causes that have resulted in the forma- 

 tion of the bud, certainly its closely united scales which are often 

 reinforced with resinous, mucilaginous or hairy coatings, are an 

 admirable device for protecting the delicate parts within against 

 winds which would rob them of water at a time when none could 

 be obtained from the soil. It is quite natural to think of these 

 devices as protection against cold, but strangely there is no adap- 

 tation known among plants that serves primarily as a protection 

 against low temperatures, and there is no cold upon the earth 



