224 BIOLOGY. 



posed in circles, and so united by a thin cellular integu- 

 ment or membrane, that the whole forms a vesicle. 



1126. This vesicle is a Bud. A bud is at bottom 

 none other than the end of a twig that has become 

 hollow. 



1127. Several buds are usually involved in each other, 

 i. e. many vesicles of tracheal rings have been encased 

 in each other. They issue gradually forth and become 

 shoots or buds. Buds are bulbs at the end of the 

 branches. 



Leaves. 



1128. If the bud or the external vesicle ruptures, 

 while the cellular substance becomes consumed at the 

 apex or between two or more tracheal fascicles, it is then 

 manifested as a leaf or Leaves. 



1129. Then the second vesicle grows forth, becomes 

 petiolated, ruptures and becomes leaf or leaves. In 

 this manner a twig is formed, surrounded in a spiral 

 manner by leaves. 



1130. The younger leaves have been originally in- 

 closed in the older, as in their sheaths. 



1131. Every perfect leaf, i. e. every leaf- vesicle, must 

 be regarded as the terminal extremity of an entire twig, 

 from or out of the angle of which a new twig grows 

 forth, that again as a bud ruptures, and from which 

 again a twig grows forth. 



1132. All leaves therefore range directly opposite to 

 each other. A branch with many leaves is a system of 

 branches, which grow out of each other, like the arti- 

 cular pieces of the grass-culm or straw. 



1133. A leaf is a whole plant with all its tissues and 

 systems ; with cells, ducts, tracheae ; bark, liber, wood, 

 stalk and branches. The leaf is a tree of special form, 

 a tree, whose branches or tracheal fascicles all lie in one 

 plane and are held together by parenchyma. It is the 

 bodily expression of the position of the tracheal circle 

 in the stem, only ruptured and to the greatest degree 

 attenuated. 



