OF BUDS. 291 



acts the part of a "bud ; sometimes it surrounds it so 

 completely, that no bud is perceived in the axil, but it 

 appears lodged in a cavity of the petiole formed by the 

 two edges of the sheath folded upon one another. This 

 is seen very clearly in Smilax aspera, where the peti- 

 olary sheath surrounds the young shoot, and remains 

 upon it until the spring. We meet with an analogous 

 and still more singular fact in the Plane ; here the leaves 

 fall off in the Autumn, so that the bud is not protected 

 as at its first development : the margins of the petiolary 

 sheath are completely united together so as to seem to 

 inclose the bud ; but if we make an examination just 

 before the fall of the leaves, we see that the base of the 

 petiole is split longitudinally on the upper side, exactly 

 at the place where the theory indicates that the two 

 margins of the sheath ought to be found. Phenomena 

 analogous to the preceding are met with, with slight 

 variations, in Negundo, Pkiladelphus, Robinia, and some 

 species of Sumach (Rhus). 



The buds which are developed in perennial herbs, 

 either on a level with the surface or under ground, differ 

 the more from aerial ones, in proportion as they are 

 more decidedly subterranean. The more a vegetable 

 surface is deprived of the action of air and light, the 

 paler will it be, the less will it evaporate, and conse- 

 quently it will take, according to the texture of its 

 organ and the period of its vegetation, either the appear- 

 ance of a simple membrane, or that of an etiolated body, 

 but, however, full of juice. 



If we compare the aerial buds of the tree Poeony 

 with those at the neck of the herbaceous ones, (PL 15, 

 Fig. 1, 2, 3,) it will be impossible to perceive any other 

 differences between them than those which result from 

 their position ; and all the turiones, or buds on a level 

 with the ground, in perennial non-bulbous plants, hardly 



u 2 



