42 EXOGENS AND KNDOGENS. 



after the same manner, is distributed into " genera," and every 

 "genus" into a less or greater number of "species," which are made 

 up of thousands and millions of " individuals." It is much the same 

 as in geography, where we first have continents, then countries, then 

 provinces, then parishes, then towns, streets, houses, and inhabitants. 

 On a very slight acquaintance with flowering plants, it is discovered 

 that some possess ?je^veined leaves, and the remainder straight or 

 jiarallel-yeined ; further, that when the leaves are net- veined, the 

 parts of the flower are in Jives or fours, and when parallel-veined, in 

 threes. Further again, that the stems of the net-leaved plants are 

 composed of distinct bark, wood, and pith ; while in the parallel- 

 veined there is no such distinction, the woody portion being com- 

 mingled with the pithy, and bark entirely wanting : and lastly, that 

 the seeds of the net-leaved plants contain two embryo leaves, which, 

 at the period of germination, usually lift themselves above the ground, 

 and spread horizontally ; while those of the parallel- veined contain 

 but one leaf, which, at germination, shoots up vertically, like a blade 

 of sprouting corn. However trifling the two sets of characters may 

 appear when stated in words, they are exponents of a thorough 

 difierence in every particular, both of structure and aspect. The two 

 classes which they mark are called respectively Exogens and Endo- 

 GENS, the names referring proximately to the mode in which the stem 

 increases in substance and solidity, every plant that bears a flower 

 belonging to one or the other, and plainly declaring which.* True, 

 there are in both classes departures from the typical structure, and 

 indiAiduals, and sometimes entire families, curiously mimic the shapes 

 of the other ; but on the whole, the peculiar characters are constant 

 and prominent, or at least sufficiently plain for practical purposes. 

 One part or another is always in the fi'ont. If the leaves fail to shew 

 whether the plant be an Exogen or an Endogen, it is told by the 

 flower ; and if the flowers refuse to speak, it is told by the stem or 

 seed. With the aid of the diagram opposite, the two classes will 

 readily be conceived. 



• By Bome botanists they are called '' Dicotyledones " and " Monofotyledones." 



