Dec, 1906.] THE VICTORIAN NATURALIST. 147 



up and turgid with Saj), do hereby press upon it, and so not only 

 a little contract its bore but also transfuse or strain some Portion 

 of their Sap thereinto ; by both which means the Sap will be 

 forced to rise higher therein. And the said Pipe or Vessel being 

 all along surrounded by the like Bladders, the Sap therein is still 

 forced higher; the Bladders of the Parenchyma being, as is said, 

 so many Cisterns of Liquor, which transfuse their repeated sup- 

 plies into the Vessel. So that by the supply and pressure of the 

 Cisterns or Bladders F D, the sap riseth to L ; by the Bladders 

 Q L it rises to M ; by the Bladders N M it rises to I, and so to 

 the top of the Tree. And thus far of the motion of the Sap." 



This is a very remarkable account, considering the physical 

 knowledge of the time, and that the laws of osmosis, as well as the 

 existence of a " primordial utricle " within the cell-wall had yet to 

 be discovered, while the high cohesion of a suspended continuous 

 column of water was not even suspected. We have made com- 

 paratively little advance in essentials since Grew's time, in spite of 

 the host of workers whose energies have been directed to the solu- 

 tion of these problems. Without using any special term to denote 

 the phenomena of imbibition, Grew clearly held, on experimental 

 grounds, that imbibition alone was insufficient to produce the 

 ascent of the sap, and in this respect his ideas were more correct 

 than those of Sachs. 



Grew regarded spiral vessels as of especial importance for the 

 conveyance of air, although he also states that intercellular spaces 

 aid in the process, and that they become of especial importance 

 for the aeration of water-plants. The abundance of spiral vessels 

 in leaves was noticed, and also the unravelling of a spiral thread 

 from the vessels of a torn leaf — a ready method of demonstration 

 which is in use at the present day. As regards the entrance of 

 air, Grew assumed that it was absorbed mainly by the root 

 and pressed upwards with the transpiration current, though he 

 observed the existence of pores on stems and stomata on 

 leaves, and states that a certain amount of air enters by these 

 means. The error arises from the attempt to compare the root 

 of a plant with the mouth of an animal ; and, indeed, many of the 

 older botanists regarded a plant as comparable with an animal 

 standing upon its head, so that had the life-history of any 

 cirrhipede, such as Balanus or Lepas, been known it would have 

 been regarded as an example of direct metamorphosis from an 

 animal to a plant. 



Among a variety of miscellaneous observations made by Grew 

 the following are worthy of notice : — A distinction is drawn 

 between vessels bearing clear sap (p. 67) and those with milky 

 sap (lactiferous tubes, p. 86). The weathering of soil is 

 mentioned (p. 81), the importance of humus recognized, and 

 also the loss of the volatile products of decomposition in exposed 



