THE STRUCTURE AND WORK OF THE STEM 111 



II 



steps in tongue grafting. 



(a) the two branches to be 

 joined ; (6) a tongue cut in 

 each ; (c) how fitted together ; 

 (d) method of wrapping. 



ing spring, it is found to have all the characters of the tree from 

 which it was taken. This proccs.s is known as budding. 



Grafting. — Of much the same nature 

 is grafting. Here, however, a .small 

 portion of the stem of the closely allied 

 tree is fastened into the trunlv of the 

 groT\dng tree in such a mamier that the 

 two cut cambium layers \\'ill coincide. 

 This will allow of the passage of food 

 into the grafted part and insure the 

 ultimate growth of the twig. Grafting 

 and budding are of considerable eco- 

 nomic value to the fruit grower, as it 

 enables him to produce at will trees 

 bearing choice varieties of fruit.' 



In both of the above processes, the secret of successful growth 

 lies in the fact that the cambium surface of the bud or the graft 

 comes in contact with the cambium of the tree to which they are 

 applied, thus putting them in direct communication with a supply 

 of food from the already established tree. 



Modified Stems. — We have seen in previous experiments, external 

 forces may act on the organs of a plant so as to change its appearance 



and often its form and habit. A stem 

 grown in complete darkness is white 

 instead of green. The bleaching of the 

 celery stems by cohering them is a 

 familiar example of this. Thus, in na- 

 ture, forces which we know of as light, 

 gravity, heat, moisture, \\ind, and per- 

 haps other factors, influence the plant 

 in its growth. Thus changes may take 

 place which fit or adapt the parts of a 

 plant better for life under certain con- 

 ditions in which it must exist. 



Stems modified for Water or Feed 



Storage. — Many stems store large 



quantities of food. The sago palm is 



an example of such a stem. In most woody stems food is stored during 



some parts of the year and is used as the plant comes to need it. In 



' For full directions for budding and grafting, see Goff and Mayne, First Princi- 

 ples of Agriculture, Chap. XIX, or Hodge, Nature Study and Life, pages 169-179. 



The potato tulxT a stem ; note the 

 branches growing from the "eyes" 

 at one end. 



