SKELETON OF THE LEAF. 155 



the secondary veins of Exogens, however they may be disposed, 

 always give off a vast number of minute branches, which ramify 

 and unite with each other, so as to form a complete network ; 

 and thus it is, that the leaf of an Exogen can seldom be torn 

 with any regular edge. From this character, the Exogens 

 may be described by their leaves, as reticulated-veined; the 

 veins forming a reticulum, or minute net- work. 



233. It is in these that we can make the most beautiful 

 skeletons, by removing the soft fleshy portion of the leaves, and 

 preserving only the woody structure. Such skeletons may often 

 be found in the autumn, when the fallen leaves have been 

 exposed to the influence of moisture for some time ; and with 

 slight care, they may be made to exhibit a very beautiful 

 appearance. They may easily be prepared, by soaking in water 

 a leaf possessed of firm texture, until its softer portion be in a 

 state of decay ; if then the latter be washed away, by carefully 

 directing a small stream of water against it, the skeleton will 

 be left. Not only do leaves contain such a skeleton ; but the 

 leafy parts of flowers ; and even the skins of such soft fruits as 

 the cherry. 



234. Now, with the same distribution of the veins of the 

 leaf, many curious varieties of structure may be produced, by a 

 difference in the degree in which the space between them is filled 

 up. One of the simplest of these, is where holes are left in the 

 blade of the leaf, in consequence of a deficiency of the fleshy 

 portion. Some plants are particularly liable to this irregularity; 

 which does not exist, however, where they are well supplied 

 with nourishment. A similar, but much more curious variety 

 exists in an aquatic plant of Madagascar ; in which the fleshy 

 cellular tissue, or parenchyma, is so little developed between the 

 veins, that the living leaf much resembles in its form one of the 

 skeletons just described. 



235. It is by no means uncommon, to see the edges of leaves 

 more or less deeply indented, according to the amount of nutri- 

 ment which the plant is receiving; the distribution of the veins, 

 and the general outline of the leaf, remaining the same through- 



