L^SSCN 9.] 



PERFOLIATE LEAVES, ETC- 



67 



are bipinnate, i. e. twice pinnate, as in Fig. 130. If these leaflets 

 were again divided in the same way, the leaf would become thrice 

 pinnate, or tripinnate, as in many Acacias. The first divisions are 

 called pinnae ; the others, pinnules ; and the last, or little blades, 

 leaflets. 



172. So the palmate leaf, if again compounded in the same way, 

 becomes twice palmate, or, as we say when the divisions are in 

 threes, twice ternate (in Latin form Uternate) ; if a third time com- 

 pounded, thrice ternate or triternate. But if the division goes still 

 further, or if the degree is variable, we simply say that the leaf is 

 decompound ; either palmately or pinnately so, as the case may be. 

 Thus, Fig. 138 represents a four times ternately compound, in other 

 words a ternately decompound, leaf of our common Meadow Rue. 



173. So exceedingly various are the kinds and shapes of leaves, 

 that we have not yet exhausted the subject. We have, however, 

 mentioned the principal terms used in describing them. Many 

 others will be found in the glossary at the end of the volume. Some 

 peculiar sorts of leaves remain to be noticed, which the student might 

 not well understand without some explanation ; such as 



174. Perfoliate Leaves, A common and simple case of this sort is 

 found in two species of Uvularia or Bellwort, where the stem appears 

 to run through the blade of the leaf, 



near one end. If we look at this plant 

 in summer, after all the leaves are 

 formed, we may see the meaning of this 

 at a glance. For then we often find 

 upon the same stem such a series of 

 leaves as is given in Fig. 131 : the low- 

 er leaves are perfoliate, those next above 

 less so ; then some (the fourth and fifth) 

 with merely a heart-shaped clasping 

 base, and finally one that is merely 

 sessile. The leaf, we perceive, becomes 

 perfoliate by the union of the edges of 

 the base with each other around the 

 stem ; just as the shield-shaped leaf, Fig. 

 102, comes from the union of the edges of the base of such a leaf 

 as Fig. 101. Of the same sort are the upper leaves of most of 



FIG. 131. Leaves of Uvularia (Bellwort) ; the lower ones perfoliate, the others merely 

 clasping, or the uppermost only sessile. 



