146 THE VICTORIAN NATURALIST. [Vol. XXIII. 



and elaborate it for use by the flowers and fruits, while later on 

 (p. 82) it is mentioned that dilute solutions of salts are absorbed 

 from the soil by the roots. According to Grew the sap thus 

 obtained is " strained " in passing through the epidermis, and 

 distends' the " bladders " of the parenchyma to the utmost 

 possible extent. These are not openly pervious, and hence the 

 sap is " strained " a hundred times over in its passage from 

 bladder to bladder. The different tissue elements will absorb 

 various constituents of the sap, and at the same time the latter 

 will receive other substances from them, so that it may be much 

 altered in its passage upward (p. 83). Grew's ideas upon the 

 ascent of water are extremely interesting, and have anticipated 

 Godlewski's and Westermain's pumping action theory by a couple 

 of centuries, for in one point only is Grew certainly in error — 

 namely, when he supposes that the turgid parenchyma pressing 

 upon the vessels will cause them to contract, so that a rhythmic 

 repetition of this pressure would pump the water upwards. It is 

 obvious that Grew was unaware of the rigidity and elasticity of 

 the walls of the trachea and tracheides, but, nevertheless, his 

 remarks are interesting on this point, since they clearly indicate 

 that he understood and had observed the existence of positive 

 and negative tissue tensions in plants (p. 84, &c.) This is how 

 our author sums up (p. 126) : — 



13 §. " From what we have now above and elsewhere formerly 

 said, we may also understand the manner of the Ascent of the 

 Sap. As to which I say, First, That considering to what height 

 and plenty, the sap sometimes ascends, it is not intelligible, how 

 it should thus ascend by virtue of any one part of a plant alone ; 

 that is neither by virtue of the parenchyma nor by virtue of the 

 vessels alone. Not by the ^xirenchyvia alone. For this, as it 

 hath the Nature of a Sponge or Filtre to suck up the sap, so 

 likewise to suck it up but to a certain height, as perhaps to about 

 an inch or two and no more."* 



14 §. " Nor by the Vessels alone for the same reason. For 

 although we see that small Glass-Pipes immersed in water will 

 give it an ascent of some inches, yet there is a certain period, 

 according to the hore of the pipe, beyond which it will not rise. 

 We must therefore joyn the Vessels and the Parenchyma both 

 together in this Service, which we may conceive performed by 

 them in the manner following." 



15 §. " Let A B be the Vessel of a Plant. Let C E D F be 

 the Bladders of the Parenchyma, wherewith, as with so many 

 little cisterns, it is surrounded. I say then, that the sap, in the 

 pipe B A, would, of itself, rise but a few inches ; as suppose from 

 D to L. But the Bladders D P, which surround it, being swelled 



* C/. Pfeffer, "Physiology of Plants," 1900, p. 210 (Transference of water 

 through parenchyma). 



