22 PROPAGATION BY MEANS OF ROOTS AND STEMS 



fast to it; and if its original trunk die away, the part will 

 be growing on an alien root. A branch that grows fast 

 to a branch of another plant, the wood of the two knitting 

 together, is called a graft. (Fig. 32.) It is necessary to dis- 

 tinguish between a graft and a parasite: a parasite preys 

 upon another plant, robbing it of its food, but a graft becomes 

 an integral part of the stock on which it grows, and does 

 its full work in elaborating food for itself and for the stock. 



Review. — What are primary and secondary functions of roots and 

 stems? What are the functions of rhizomes? How does propagation 

 by rhizomes proceed? Why does the colony spread? Name some plants 

 that propagate by means of rhizomes. What is a cutting? May cuttings 

 be made of rhizomes? How are rhizomatous weeds often spread? 

 Name some of them. How do roots serve to propagate the plant? Name 

 instances. What are adventitious buds? What is a layer? Define some 

 of the kinds of layers, — runner, creeper, stolon, offset. Explain how 

 cuttings may occur without the aid of man. How may leaves serve 

 to propagate the plant? Explain how plants propagate themselves by 

 means of detachable buds. What is a graft? How may grafting take 

 place without the aid of man? 



Note. — If there is an accessible "patch" of toad-flax, Canada 

 thistle, may-apple, or other perennial plant, the pupil should determine 

 by what means it enlarges from year to year. "Patches" are always 

 instructive when considered with reference to propagation and dis- 

 semination. 



