92 



THE PLAOTER's guide. 



plijtologists, is termed introsiisception ; and the former 

 mode, of com^se, applies to the iutrosusception of non- 

 elastic fluids, and the latter to that of gaseous fluids.'" 

 The fact is, that the roots are much rather to be regarded 

 as the mouths of plants, selecting what is useful to nour- 

 ishment, and rejecting what is jet in a crude and indiges- 

 tible state ; the larger portion of it also serving to fix the 

 plant in the soil, and to convey to the trunk the nomish- 

 ment absorbed by the smaller fibres, which, ascending by 

 the tubes of the alburnum, is thus conveyed to the leaves.f 

 Roots, moreover, by their vigour and numbers, must pre- 

 viously stretch out under ground before the branches can 

 extend themselves in the air; and the progress of the 

 latter development will, of com'se, be in proportion to that 

 of the former. By the cmious and beautiful way in which 

 almost every part of a tree modifies and determines the 

 existence of every other part, as above noticed, the roots 

 in their turn receive vigour and extension from the ad- 

 vancement of the branches. 



It appears that roots and fibres are found more or less 

 extensive in the ratio of the exposure or shelter in which 

 a tree is placed. In open situations they are always 

 strong and numerous, and they extend to a wide distance 

 from the plant. This is indispensably necessary, not- 

 Avithstanding the short and powerful stem which a tree so 

 situated usually displays, in order to enable it to resist 

 the elements, and to provide sustenance for the great 

 expansion of top with which such a tree is sure to be fur- 

 nished. Hence may be seen the great importance of 

 numerous roots and fibres in removing trees of any mag- 

 nitude. It is supposed by some that the roots of trees so 

 placed, if of considerable age, after having exhausted 



* Note III. f Keith, vol. ii. p. 246 ; also pp. 90, 250. 



