26 PLANTS 



54. In those cases in which the cotyledons appear above the 

 ground they serve to protect the delicate plumule while the 

 vigorous hypocotyl is pushing it up through the earth. If the 

 cotyledons in this case are greatly thickened they are likely to 

 become shriveled as they give up their food to the seedling, 

 and finally they may fall off. Again they may become green 

 and serve for a time the functions of leaves. Very often they 

 are clearly leaflike at the beginning and remain for some time 

 as the first pair of leaves. In every case the cotyledons nourish 

 the seedling, either from endosperm or perisperm, or from the 

 food contained within their own tissues, until green leaves are 

 developed by transformation of the cotyledons themselves or 

 by the development of the first leaves by the plumule. 



55. The plumule is the last of the embryonic parts to begin 

 its development. From it arise practically all the above- 

 ground parts of the plant, i. e., stem and leaves. In the embryo 

 it is essentially a bud, and, as it develops, one segment of the 

 stem after another appears and leaf after leaf unfolds until we 

 have the fully formed plant. The region of development, i. e., 

 the formation of new parts, in the plumule is at the apex of 

 its axis in the center of the bud, but after the parts have been 

 formed and unfolded they continue to expand for some time. 

 From this primary bud, which is first called the plumule, but 

 later on is known as the terminal bud, is developed, directly, 

 the main axis or stem of the plant with its leaves. 



56. Secondary axes, or branches, are developed from buds 

 (axillary buds) which appear in the angles (the axil) between 

 the leaves and the stem. In the case of perennial plants the 

 leaves which form last, but do not unfold in the fall, and which 

 are the first to unfold in the following spring, are scale-like in 

 form and serve to protect the tender parts which they enfold, 

 from the winter weather. 



57. In some cases accessory buds occur above or on either 

 side of the axillary bud, and adventitious buds may occur on 



