84 ROOTS OF PLANTS. 



has been said by some authors that the roots of trees 

 spread as much beneath the ground as the branches 

 do above it; but this can hardly be said to hold 

 good in all cases. Fibrous-rooted plants often per- 

 form great service in loose sandy soils, especially 

 along water-courses, where they form a thick and 

 matted mass, thus preventing the washing away of 

 the earth. Tuberous roots are solid and very irregular 

 in their shape, and are often linked together by slen- 

 der fibres. Roots of this form are the most useful, as 

 they are generally edible; the common potato, the 

 turnip, and the radish, are familiar examples. 



Bulbous roots are of various kinds ; some are solid, 

 as in the crocus ; others are composed of fleshy layers 

 placed one above the other, as in the onion ; and others 

 consist of thin scales, as in some species of the lily. 

 They all appear to act as reservoirs for the vitality 

 of the plant during its dormant state. 



A bulb is entirely analogous to the bud upon a 

 tree, each containing within itself the embryo of the 

 future stem or plant. In the bulb of the tulip, the 

 microscope will reveal the entire leaf, stem and flower, 

 all folded up within its layers, and which require no- 

 thing but the action of light, heat and moisture, to 

 expand into perfection ; so in the bud upon the tree, 

 the leaves and blossoms which open in the spring are 

 all encased in miniature in that tiny compass. 



