228 VEGETABLE ORGANOGRAPHY. 



as the Fir, has its roots smaller, not only relatively, 

 but in certain situations absolutely speaking, than the 

 Lucerne or such other smaller herb than itself. 



Generally, spindle-shaped roots do not descend beyond 

 a few feet in depth, because below this limit they either 

 meet with strata of earth too hard for them to pierce, or 

 they cannot sufficiently enjoy the influences of the atmo- 

 sphere. 



Some spindle-rooted plants, such disEryngium, although 

 their root is sometimes found buried at a very great depth, 

 do not form a real exception to this rule ; for more fre- 

 quently, especially on downs, as I have said above, it is 

 the earth which is elevated, and not the plant which has 

 descended ; and the greatest part of that which is taken 

 for the root is formed by true stems, to which their re- 

 maining underground has given the appearance of roots. 



Horizontal or creeping roots, being situated in such a 

 manner as to be prolonged into lighter earth, and near 

 the influences of the atmosphere, are those which take 

 the greatest dimensions in length ; thus the roots of the 

 Elm, Rohinia pseud-acacia, Ailantus or Sumach, are 

 sometimes prolonged some hundred feet beyond the 

 trunks which gave origin to them ; they are seen to in- 

 sinuate themselves under buildings, between the cracks 

 of walls, and often to produce extraordinary dilapidations 

 at a great distance from their origin : when the young 

 radical fibrils creep into the imperceptible cracks of rocks 

 or walls, and as they there find a favourable nourishment, 

 they are slowly developed, but with sufficient force to 

 raise up enormous weights, and to move masses which 

 would seem immovable. When roots are but little 

 branched, or divided into fibres too thick to insinuate 

 themselves into cracks, or when they meet with invin- 

 cible obstacles, it happens either that the root takes a 

 very different direction from its usual one, or that the 



