The Anatomy and Physiology of Plants 61 



section where palm trees grow, but all of our grasses have 

 some such structure. Indian corn, really a grass, is a 

 good example. Break off a dry stalk of corn and you will 

 find a multitude of the thread-like forms growing up 

 through the soft fundamental tissue. If we make a thin 

 cross-section of a corn stalk and examine it under a micro- 

 scope we shall see that these threads are really tubular in 

 form and are the means through which each leaf on the 

 corn plant gets the water from the soil. Not that the soil 

 water comes up in these tube-like structures in the same 

 way that water runs through a pipe, for the elongated cells 

 are really filled with air and the water rises by permeating 

 the walls of the cells. 



These two classes of plants have been denominated, 

 the first class exogens or outside growers, and the second 

 class endogens or inside growers. While these names are 

 not scientifically accurate they serve very well to distin- 

 guish the characters of the plants. The differences in 

 their structure are correlated with other differences, be- 

 ginning from the structure of the flowers, the germination, 

 and the general habit of the plants. The better distin- 

 guishing terms would be to call the first class, the exogens, 

 dicotyledons, because of the fact that in germinating from 

 the seed they always have a pair of seed leaves, while the 

 other class or endogens, are very properly monocotyle- 

 dons, or one-seed-leaf plants. The seed leaves are termed 

 cotyledons by botanists, and with the prefix, monOy the 

 word means of one, and with di, of two, seed leaves. 

 There is still another class with which we have little to 

 do in agriculture, which make a circle of seed leaves 

 in germinating, and is therefore called poly, or many 



