AND GERMEN DURING VEGETATION. 129 



it penetrates. The true sap also continues to descend from the cotyle- 

 dons and leaves, and occasions a continued increase of the growth of 

 the upper parts of the radicle, and this growth is subsequently aug- 

 mented by the effects of motion, when the germen has risen above the 

 ground. The true sap is therefore necessarily obstructed in its descent ; 

 numerous lateral roots are generated, into which a portion of the 

 descending sap enters. The substance of these roots, like that of the 

 slender horizontal branches, is much less succulent than that of the 

 radicle first emitted, and they are in consequence less obedient to gravi- 

 tation : and therefore, meeting less resistance from the superficial soil 

 than from that beneath it, they extend horizontally in every direction, 

 growing with most rapidity, and producing the greatest number of rami- 

 fications, wherever they find most warmth, and a soil best adapted to 

 nourish the tree. As these horizontal, or lateral roots surround the 

 base of the tree on every side, the true sap descending down its bark, 

 enters almost exclusively into them, and the first perpendicular root, 

 having executed its office of securing moisture to the plant, whilst young, 

 is thus deprived of proper nutriment, and, ceasing almost wholly to grow, 

 becomes of no importance to the tree. The tap root of the oak, about 

 which so much has been written, will possibly be adduced as an excep- 

 tion ; but having attentively examined at least 20,000 trees of this spe- 

 cies, many of which had grown in some of the deepest and most favour- 

 able soils of England, and never having found a single tree possessing a 

 tap root, I must be allowed to doubt that one ever existed. 



As trees possess the power to turn the upper surfaces of their leaves, 

 and the points of their shoots to the light, and their tendrils in any 

 direction to attach themselves to contiguous objects, it may be suspected 

 that their lateral roots are by some means directed to any soil in their 

 vicinity which is best calculated to nourish the plant, to which they belong; 

 and it is well known that much the greater part of the roots of an 

 aquatic plant, which has grown in a dry soil, on the margin of a lake or 

 river, have been found to point to the water ; whilst those of another 

 species of tree which thrives best in a dry soil, have been ascertained to 

 take an opposite direction : but the result of some experiments I have 

 made is not favourable to this hypothesis, and I am rather inclined to 

 believe that the roots disperse themselves in every direction, and only 

 become most numerous where they find most employment, and a soil best 

 adapted to the species of plant. My experiments have not, however, 

 been sufficiently varied, or numerous, to decide this question, which I 

 propose to make the subject of future investigation. 



