iESSON 7.] MORPHOLOGY OF LEAVES. 49 



LESSON VII. 



MORPHOLOGY OF LEAVES. 



117. IN describing the subterranean forms of the stem, we have 

 been led to notice already some of the remarkable forms under 

 which leaves occur ; namely, as scales, sometimes small and thin, as 

 those of the rootstocks of the Quick-grass, or the Mint (Fig. 64), 

 sometimes large and thick, as those of bulbs (Fig. 73-75), where 

 they are commonly larger than the stem they belong to. We have 

 seen, too, in the second Lesson, the seed-leaves (or cotyledons) in 

 forms as unlike foliage as possible ; and in the third Lesson we have 

 spoken of bud-scales as a sort of leaves. So that the botanist recog- 

 nizes the leaf under other forms than that of foliage. 



118. We may call foliage the natural form of leaves, and look 

 upon the other sorts as special forms, as transformed leaves: by 

 this term meaning only that what would have been ordinary leaves 

 under other circumstances (as, for instance, those on shoots of Mint, 

 Fig. 64, had these grown upright in the air, instead of creeping under 

 ground) are developed in special forms to serve some particular 

 purpose. For the Great Author of Nature, having designed plants 

 upon one simple plan, just adapts this plan to all cases. So, when- 

 ever any special purpose is to be accomplished, no new instruments 

 or organs are created for it, but one of the three general organs of 

 the vegetable, root, stem, or leaf, is made to serve the purpose, and 

 is adapted to it by taking some peculiar form. 



119. It is the study of the varied forms under this view that con- 

 stitutes Morphology (61), and gives to this part of Botany such great 

 interest. We have already seen stems and roots under a great 

 variety of forms. But leaves appear under more various and widely 

 different forms, and answer a greater variety of purposes, than do 

 both the other organs of the plant put together. We have to con- 

 sider, then, leaves as foliage, and leaves as something else than foliage. 

 As we have just been noticing cases of leaves that are not foliage, 

 we may consider these first, and enumerate the principal kinds. 



120. Leaves as Depositories of Food. Of these we have had plenty 

 of instances in the seed-leaves, such as those of the Almond, Apple- 



