THE LEAVES OF VASCULAR PLANTS. 281 



that the upper are opposite or verticillate. If the leaves 

 which compose each spire are very near together, and 

 at the same time the interval between each system is 

 well marked, the spire, becoming very short, resembles 

 verticillate leaves, as in Convallaria verticillata, — or 

 opposite ones, as in Dioscorea. When these leaves are 

 sheathing, we clearly see that they are not really oppo- 

 site, but that one is a little above the other, as in the 

 glumes of the Glamineae. 



Thus, when we considered the Stem, we observed that 

 there was a remarkable connexion between its structure 

 and the number of cotyledons ; in the same manner we 

 may here establish a general law, that in Dicotyledons 

 the leaves are primordially opposite or verticillate, but 

 may become alternate or spiral in consequence of their 

 mode of growth ; and that in Monocotyledons they are 

 primitively alternate or spiral, but may become more or 

 less opposite or verticillate in their successive develop- 

 ment ; whence it results, consequently, that every plant 

 which has the lower or primordial leaves alternate or in 

 a spire, is a Monocotyledon, even when the upper ones 

 are opposite or verticillate. 



The leaves of both classes may appear to arise in 

 bundles, and are said to be Fasciculate, from some of 

 the following causes : — 



1st. Compound leaves may have the common petiole 

 so short, that the leaflets seem to arise in a bundle from a 

 common base, as in Aspalathus. 



2d. It sometimes happens that the true leaf is either 

 wholly or partly abortive, and at the same time the 

 branch which is developed in its axil remains very short, 

 and furnished with small leaves ; this takes place in the 

 Barberry, the spire of this shrub being the rudiment of 

 its true leaf, and those which are called leaves are axil- 

 lary leaflets, crowded upon a very short brancli. This 



