4 THE HUMAN SIDE OF PLANTS 



spring from their parent stem underground and 

 later appear as separate plants ; and eventually the 

 little connecting link or thread may be entirely de- 

 stroyed. It is in this way "by root," as we say- 

 that raspberry bushes increase or spread out. 



Many grasses spread in the same way, and in all 

 directions; some have joints from which upright 

 stems arise, and which send down into the earth 

 roots of their own, interlacing and binding the soil 

 and thus spreading very rapidly. Such grasses 

 grow several feet in a few months. The quack- 

 grass is a typical example of a fast walker and for 

 this reason is greatly feared by farmers. 



Tulips are noted for their ability to walk. If 

 planted in dark, shady places, where it is cold and 

 damp, they will deliberately walk away from the 

 dark place into a more desirable part of the garden. 

 They usually move into the sun. The bulb that 

 was planted does not itself actually move, but its 

 substance is transferred little by little, and only the 

 outer wrapping of brown tissue is left. The bulb 

 sends out a delicate shoot that runs horizontally 

 below the ground until it has reached a distance of 

 several inches. Then, near its point, a swelling 

 begins to take the shape of a tulip bulb, which 

 grows larger and larger as the food-material of 

 the old bulb is brought into it. This is done by 



