Botany, 



463 



convey any distinct meaning, nor apply to a definite class of substances, 

 The recent brilliant discoveries in vegetable chemistry ought to put an end 

 to this vague phraseology. — J. R. 



Influence of Soil on Roots. — " If a cucumber," says Sir James Smith in 

 his Lectures, of which MS. notes are now before me, " is planted; and 

 after the branches shoot there is placed a stone in the way of either of 

 them, the branch will turn off and avoid it without touching the stone, but 

 describing a circle around it. When it has passed the stone, however, it 

 will go on in a straight line." Sir James explains this by the well-known 

 law of plants always approaching the light, the cucumber turning round ta 

 get out of the shadow of the stone. 



Roots follow a very different law, always endeavouring to get away from 

 the light ; and, accordingly, so far from avoiding a stone or other obstacle, 

 they often cling closely around it, 

 and sometimes even mould their 

 forms upon the hard substances 

 with which they meet. This is well 

 exemplified in the root of an alder 

 tree(^'lnus glutinosa, Betula J'lnus 

 Lin7i.), which my little boy found 

 in his searches after fresh-water 

 shells for his collection. (See Vol. I. 

 p. 413.) The root (fg. 115 a) was 

 embedded among the gravel form- 

 ed by theRavensbourne river which 

 passes the bottom of my garden ; 

 and it requires no details to point 

 out how exactly it has moulded 

 itself on every stone which it met 

 with in its course. In the same 

 manner roots are much influenced 

 in their forms by the soils in which 

 they grow. Of this I lately gave 

 the following illustration in the 

 AthencDum, from the familiar in- 

 stance of fibrous and bulbous 

 roots: — When plants with fi- 

 brous roots are placed in certain 

 situations, they are apt to change 

 their fibrous structure for a bulb- 

 ous one, in the same way as the 

 water crowfoot (iJanunculus aqua- 

 tilis) has scolloped leaves above, 

 and minutely winged leaves below, 

 water. The change from fibrous 

 to bulbous roots, and the contrary, 

 is markedly exemplified in some 

 of the grasses, particularly in Ti- ^ _ _ 

 mothy grass (Phleum) and fox-tail gras"s'(^'iopecurus). Before this change 

 of form was discovered, botanists frequently described the same grass under 

 different names ; a circumstance which occurred with regard to ^lopeciirus 

 geniculatus (6) and Phleum pratense (c). Leers seems to have been the first 

 to discover that transplanting into a light rich soil tends to change the 

 bulbous into the fibrous structure. — J.Rennie. 



Descent of the Radicles in the Germination of Seeds. — The unsatisfactory 

 nature of several of the theories hitherto proposed on this subject has been 

 ably shown by H. Johnson, Esq., in a paper read before the Medical Society 



H H 4 



