282 ABSORPTION OF LIQUIDS THROUGH ROOTS. 



without laceration of the delicate cells. Notwithstanding the 

 extreme tenuity of the cell-wall, it is thought by some to play an 

 important mechanical part in fastening the roots in the soil. 1 



624. That the hairs upon the root vastly increase its absorb- 

 ing surface is self-evident. Schwar/ has shown that in Indian 

 corn grown in moist air the surface presented by the velvety 

 hairs which cover the young roots is 5.5 times greater than that 

 of the part of the root on which the hairs occur ; while the ratio 

 of these surfaces in the roots of peas is as 12.4 to 1 ; and in the 

 aerial roots of Scindapsus pinnatus, as 18.7 to 1. But all these 

 figures, which are at best only approximate, appear to be very low. 



625. Extent of Root-systems. In extending, the root, by 

 growth at its protected extremity, can insinuate itself between 

 particles of soil which could not be easily displaced by simple 

 thrust. The branches from the main root extend exactly as does 

 the main root itself, by continual additions just behind the 

 tip, and the area covered by a root-system finally becomes 

 very large. One of the earliest recorded measurements is that by 

 Hales, 2 who estimated that the roots of a sunflower (3 ft. high), 

 taken together, were no less than 1,448 feet in length. The plant 

 had ''eight main roots reaching fifteen inches deep, and side- 

 ways from the stem ; it had, besides, a very thick bush of lateral 

 roots, which extended every way in a hemisphere about nine 

 inches from the stem and main roots." 



626. Nobbe has shown that in year-old plants of certain 

 closely allied gymnosperms the root-systems differ remarkably 

 in the number of the rootlets and the total length of the 

 roots. 8 In three species the determinations of the total length 

 were as follows : 



1 Haberlandt: Physiologische Pflanzenanatomie, 1884, p. 152. 



2 Hales gives as the entire surface of these roots 2, 286 square inches, or 

 15.8 square feet (Vegetable Statics, 1731, p. 6). 



3 The plants examined were grown from May to October. Two of Nobbe's 

 tables (Die landwirthschaftlichen Versuchs-Stationen, xviii., 1875, p. 279) are 

 here given : 



a. NUMBER OF ROOTLETS. 



