THE ROOTS OF VASCULAR PLANTS, 229 



entire tree is more or less raised above the soil by the 

 growth of its roots which, not being able to pierce the 

 obstacle placed before them, react upon the tree itself. 

 It is thus that we often see Palms, cultivated in tubs, 

 raise themselves up above the surface of the soil. 



Roots spread more easily in light earth ; whence it 

 results — ] st, that if individuals of the same species be 

 compared, they are the more firmly attached to the soil, 

 as the soil itself is more friable and as the trees more re- 

 quire it ; — 2d, that if different species be compared, 

 those with long roots have a greater tendency to grow in 

 light earth ; and those with short ones, which in a light 

 soil would readily be uprooted by the wind, can main- 

 tain themselves in a more compact soil. 



We have been examining the two essential functions 

 of roots viz. — those of drawing up nourishment, and of 

 fixing the plant to the soil ; it now remains for us to 

 say a few words of two less general uses, which can only 

 be carefully analyzed in Physiology. 



The first, which I have already transitorily mentioned, 

 is that several tuberous roots present deposits of nourish- 

 ment prepared beforehand, and which nourish the plant, 

 either in accidental cases, where nourishment ceases to 

 reach it ; or at periods when the leaves, not having as 

 yet been developed, are not able to elaborate it, as at 

 the commencement of spring ; or, lastly, at the time 

 when the ripening of the seeds requires a superabund- 

 ance of nutritive matter. 



Several roots, it is said, ti'ansude by their extremities 

 excrementitial juices, the origin and history of which 

 are still but little known ; but they appear to be the 

 cause of several important phenomena. These excre- 

 tions of roots have been particularly seen by Bruemans, 

 and they deserve the greatest attention on the part of 

 Physiologists. 



