404 EXOGENOUS PLANTS. PART n. 



SECTION XIV. 



DICOTYLEDONOUS, OR EXOGENOUS PLANTS. 



IN Endogenous plants the seeds have but one lobe, and 

 the growth is invariably from the interior. In the Exo- 

 genous class, on the contrary, the seeds have two lobes, 

 and the increase in growth is external : hence the bota- 

 nical distinction of Exogenous plants. Although the 

 distinctive character of the highest class of vegetables 

 is to have seeds with two lobes, yet the structure and 

 position of the seeds are extremely diversified. Many 

 have horny coats, such as the pips of apples and oranges ; 

 or hard ones, as nuts, and the stones of plums and 

 cherries. They are sometimes on the outside of the fruit, 

 as in strawberries, but oftener within it, as in the melon, 

 the pear, and a variety of others. These succulent sub- 

 stances nourish the young seeds for a time, but, when 

 they are matured, the light and heat which ripened the 

 fruits now combine to accelerate their decay and de- 

 composition, in order to set the seeds free. 



Whatever be the size or form of the seeds, whether 

 large or microscopic, they invariably contain two seed 

 lobes or primary leaves, consisting of cellular tissue, 

 between which the miniature plant, with its radicle, 

 stem, and terminal bud lies concealed. At the end of 

 the first year there is little difference in the structure of 

 a young woody plant, whether from a one or two lobed 

 seed ; the distinction begins the second year. In herba- 

 ceous plants, the stem, which is in general annual, is 

 of loose cellular tissue, with separate bundles of fibro- 



