NATURE OF PLANTS 97 



larged and fleshy, as in the Jack-in-the-pulpit, garden crocus, 

 spring beauty, etc. (Fig. 72, A). These short erect stems are 

 termed corms and are suggestive of the tuber. In other plants 

 the bases of leaves attached to the short stems function for the 

 storage of food, as in the bulb type of stems of lilies, onions, etc. 

 (Fig. 72,^). 



49. The Bud Type of Stems. The final variation of the stem 

 to which attention can be called at this time is termed the bud 

 type. The bud, as in the case of the bulb, consists of a very 

 short stem which bears a number of more or less modified leaves 

 (Fig. 73, A). The outer leaves of the bud are usually scale- 

 like and leathery and closely overlapping to protect the delicate 

 parts within. They are often further assisted in this work by 

 mucilaginous coatings and hairs, as in the horse chestnut, poplars, 

 birches, walnuts, etc. Within the scale-like leaves are the ordi- 

 nary green leaves, branches and flowers in various stages of 

 development which will appear with the opening of the buds 

 in the spring. This type of stem was doubtless induced by the 

 change of climate that followed the formation of the mountain 

 ranges and the change of the earth's orbit about the sun. As 

 soon as the tropical climate on the earth was disturbed by cold 

 currents of air that swept over the earth as a result of these 

 changes, there resulted a stunting or killing of young and im- 

 perfectly developed organs. These changes in temperature were 

 factors in producing modifications of the stem. Thus the bud 

 type came about with its closely united scales which protect the 

 delicate parts within against the drying winds which would rob 

 them of moisture at a time when none could be obtained from the 

 soil. Possibly also the buds prevent the injury that would come 

 from a too sudden freezing or thawing of the delicate parts 

 within. The rapid unfolding of the bud in the spring is a con- 

 stant source of surprise but when we recall that it contains 

 usually an abundant supply of food and practically all the organs 

 that will appear on the stem during the season we can under- 

 stand how the bud opens and elongates into a shoot bearing 

 leaves and flowers during the first few weeks of spring. The 

 part of the stem bearing the scale leaves does not elongate ma- 



