126 STEPHEN HALES 



leaf-surface ; and this is of the same order of 

 magnitude as Sachs' result/ namely, 2.2 c.c. per 

 100 sq. cm. 



He goes on to measure the surface of the roots^ 

 and to estimate the rate of absorption per area. 

 The calculation is of no value, since he did not know 

 how small a part of the roots is absorbent, nor how 

 enormously the surface of that part is increased by 

 the presence of root-hairs. He goes on to estimate 

 the rate of the flow of water up the stem ; this 

 would be 34 cubic inches in 12 hours if the stem 

 (which was one square inch in section) were a hollow 

 tube. He then allowed a sunflower stem to wither 

 and to become completely dry, and found that it 

 had lost I of its weight, and assuming that the I of 

 the "solid parts" left was useless for the trans- 

 mission of water he increases his 34 by | and gives 

 45^ cubic inches in 12 hours as the rate. But the 

 solid matter which he neglected contained the 

 vessels, and he would have been nearer to the truth 

 had he corrected his figures on this basis. The 

 simplest plan is to compare his results with those 

 obtained by Sachs^ in allowing plants to absorb 

 solutions of lithium-salts. If the flow takes place 

 through conduits equivalent to a quarter of a 

 square inch in area, the fluid will rise in 1 2 hours to 

 a height of 4+34 or 136 inches, or in one hour to 

 28.3 cm.^ This is a result comparable to, though 



^ Pflanzenphysiologie, 1865 (Fr. Trans. 1868), p. 254. 



2 He gives it as 15.8 square inches, the only instance I have 

 come across of his use of decimals. 



' Arbeiten, 11. p. 182. 



* See Sachs' Pflanzenphys. 1865 (Fr. Trans. 1868), p. 257, where 

 the above correction is applied to Hales' work. 



