BOTANY FOR YOUNG PEOPLE. 109 



and you irritate the parts and excite the germs ; 

 each germ sends downward a root, and upwards 

 a stem, and you thus have another plant. 



L. Then I suppose when the tree was turned 

 upside down the irritation was sufficient to ex- 

 cite a great many germs that gave out roots 

 below and ran upwards to the old roots to form 

 leaves and branches alone. 



E. Exactly so ; and on those facts are found- 

 ed the theory of the propagation of plants by 

 subdivision, for doing which there are three 

 modes : by layers, scions or slips, and grafts. 



L. Still I cannot exactly see why producing 

 irritation and exciting them should be sufficient 

 to cause these germs to grow. It appears to 

 me that planting seeds is the only true way of 

 raising vegetables. 



E. You can remember in one of our previous 

 conversations, I mentioned Cotyledones or little 

 cavities, which contained nutritious matter for 

 the nourishment of the young embryo or life 

 germ, that was joined to each. This little store 

 of matter, answering the same purpose for 

 the future plant, as the yolk of the egg did for 

 the young chick. Well, the principal office of 

 seed making is the enclosing of a little embryo 



