OTHER USEFUL PLANTS 69 



of roots or by cuttings. In the case of the potato, 

 nature herself has provided tubers that take the 

 place of seeds in a measure; and we have seen 

 that there is a curious reciprocal relation between 

 the formation of seeds and the formation of 

 tubers, under certain circumstances. 



In certain cases, for example, the growth of 

 the roots of a plant or even of the plant stem 

 may be promoted by the removal of the blossoms. 



We saw also how the potato that was grafted 

 on the stem of a tomato might grow aerial tubers 

 from the axils of the leaves in the position that 

 might normally be occupied by the flowers and 

 ultimately by seeds, had not the potato given up 

 the habit of seed production. 



Another illustration of the affinity between 

 bulbs and flowers is shown by the onion, which 

 sometimes grows a bulb at the top of its stalk, to 

 perform the function of seeds in storing nutrient 

 matter and at other times divides at the base 

 like many other similar plants to form offshoots 

 from which the new plant will grow another 

 season. 



But in all these cases nature is substituting one 

 means of reproduction for another, or supple- 

 menting one means with another, and the essen- 

 tial purpose of race preservation is not for a 

 moment overlooked. 



