THE ROOTS OF VASCULAR PLANTS. SS7 



complete manner, but leave the surrounding earth more 

 intact ; — 2d, that the accidents which reach their extre- 

 mity are more serious than is the case with fibrous roots, 

 since they affect at the same time all the mouths of the 

 plant. This circumstance ought to make us think that 

 tuberous roots are much more deHcate than others ; but 

 it is amply compensated by another peculiarity in their 

 structure : all of them enclose a more or less consider- 

 able deposit of nutritious matter, either feculent or mucil- 

 aginous ; whence it results that they can, in certain cases, 

 fiu-nish the plant with nourishment for some time, when 

 absorption by the exterior is stopped, just as animals 

 provided with depositions of fat can resist abstinence 

 longer than others. It is a law, usually tolerably true, 

 as to the general organization of roots, that the less 

 numerous and dispersed the spongioles are, the more they 

 present deposits of nutriment prepared beforehand. 



Spindle-shaped, or deep roots having their spongioles 

 united near the lower extremity and always having a ten- 

 dency to elongate vertically, ought to fear less than all 

 others both the severe frosts of winter and the great 

 drought of summer, because their action is exercised in 

 a stratum of earth less submitted to the influence of the 

 atmosphere. Creeping roots present the opposite ex- 

 treme ; they are more affected by too cold or too dry 

 temperatures, but they also profit more rapidly from 

 favourable atmospheric influences. 



The use of roots with regard to the manner in which 

 they fix the plant in the earth is also singularly favoured 

 by their ramifications, by which the points of attachment 

 are multiplied — by their vertical direction — or by their 

 size. In general, if individuals of the same species be 

 considered, there is a constant relation between the size 

 of the stem or branches and that of the root ; but this 

 does not exist in different species. Thus, a great tree, 



Q 2 



