THE WAY IN WHICH NEW PLANTS ARISE 137 



187. Division among the simjjle ^;?a?i^s. — Among 

 the forms in which the body consists of a single cell 

 new ones are formed by the division of a parent cell, 

 and the two halves quickly grow to the size of the 

 original cell, when they divide in turn. Such organ- 

 isms grow with great rapidity, and this method gives 

 rise to a large number of individuals in a very short 

 time. But fifteen or twenty minutes are necessary 

 to enable each cell to attain full size and divide. By 

 this method a single cell of a bacterium may produce 

 sixteen million others in eight hours, and in a day 

 many millions of millions. 



188. Runners. — Many species of seed plants 

 send out long branches with slender internodes from 

 the bases of the main stalks, and these lie on the 

 surface of the ground forming roots at each joint or 

 node. Leaves are also formed, and later an upright 

 stem. Then the runner itself dies away, leaving a 

 young plant to mark the position of each node. 

 This process may be followed in any strawberry 

 bed, and is a very efficient method of spreading the 

 plant. 



189. Stolons. — The dewberries of pastures, some 

 raspberries, and other plants, form slender stems 



