32 



INTKODUCTION TO BOTANY 



31. Reproduction by means of roots. Roots are often capable 

 of producing buds which may develop into new individuals 

 and thus propagate the plant. The sweet 

 potato is a good instance of this, each root, 

 if buried in moist sand, being capable of 

 giving rise to several new plants (fig. 24). 

 Roses are propagated by root cuttings, and 

 some trees, such as the silver-leaved poplar 

 (Populus~) and the black locust (^Robinia)^ 

 are very troublesome because of the readi- 

 ness with which young sprouts (sometimes 

 called suckers) spring up from the roots. 

 A considerable colony of these young 

 sprouts may often be seen quite surround- 

 ing the parent tree and extending many 

 feet away from it. Many bad weeds, such 

 as the field sorrel (Rumex) and the Canada 

 thistle (Cirsium), are reproduced by roots. 

 In case of desirable plants that can be 

 propagated either by pieces of root or by 

 seeds, it is generally better to use root 

 cuttings, as they will grow much faster. 



Among plants that you know, are there 

 more instances of useful or of injurious 

 kinds that are usually propagated by the 

 root? Give examples. 



FIG. 24. Vegetative 



reproduction of the 



sweet potato 



The potato was huried 

 in moist sand and began 

 to sprout, that is, to send 

 out shoots from adven- 

 titious buds at various 

 points. Each shoot may 

 grow into a new plant. 

 About half natural size 



PROBLEMS 



1. When actively growing stems are cut off, do they " bleed " on both 

 the upper and the lower cut surfaces ? Why ? 



2. How could an experiment be made to show the exact amount of 

 upward pull and of lateral pull which the anchorage of a plant will 



resist? 



3. What practical advantage is taken of the powerful anchorage of 

 shade trees ? 



4. Why must swamps be drained before most crops can be grown in 

 them? 



