40 THE LEAF. 



Fig- 84. 



JSMlK; 



Connate, Fig. 84. (growing together,) 

 at the base, so as to appear like one leaf. 

 Two opposite, amplexicaul leaves form 

 the connate. Ex. Monkey flower, (Mim- 

 ulvs ringens.) 



OBSERVATIONS ON THE LEAVES. 



The leaf is most commonly a temporary part of the plant 

 originating with the young branch which supports it, or from 

 which it grows. With the exception of evergreen plants, 

 which retain their foliage in cold climates during the winter, 

 the leaves shoot forth in the spring, flourish during the sum- 

 mer, and perish and fall to the ground towards the close of 

 autumn. A great proportion of the beauty of trees, as well 

 as much of the comfort they confer on man and animals, arise 

 from their leaves. To all phenogamous plants they are of 

 the utmost importance, being the organs by which they ab- 

 sorb from the atmosphere a portion of their nourishment. 

 The leaves of plants decompose the air, and hence they per- 

 form a similar function in the economy of vegetation, that the 

 lungs do in the animal economy. They are also the organs 

 by which the plant perspires, thus performing the same of- 

 fice for the plant that the skin does for the animal. The pores 

 by which the perspiration is emitted are on the under sides 

 of the leaves. 



The leaves ai 3 much more diversified in form, texture, and 

 composition, than any of the other vegetable organs. We 

 have seen, though in a limited degree, how they differ in 

 form, surface, situation, direction, distribution, and number. 

 Some leaves are of immense size ; while others are so small 

 as hardly to be distinguished by the naked eye. But there 

 appears to exist no proportion between the size of the leaf 

 and that of the tree to which it belongs. Thus the leaves of 

 the Oak, Birch, and Elm, though large trees, are not the fifth 

 part so large as those of the Skunk Cabbage, (Pothos fcet- 

 ida,) or Burdock, (Arctium lappa.) It is possible, however, 

 that in most cases their number may compensate for their 

 diminutive size. Thus we may observe that where the 

 leaves are small, as in the Pine, Heath, Myrtle, and many 

 other species, they are immensely numerous ; while the 



When connate ? Is the leaf a permanent or temporary part of the 

 plant ? In what respect are the leaves of plants like the lungs of animals ? 

 In what respect are they like the skin of animals ? Does there exist any 

 proportion between the size of the leaf and that of the tree? 



