340 ON THE STEM OF TRXEi. 



to it; and afterward to lend its principal aid to the forma, 

 tion of the fruit and seed. For it is this last, that is the 

 grand and finishing work of nature, to which all the rest 

 tends but as a means to the great accomplishment of pro- 

 ducing new vegetable lives. 

 The spiral ye»- The spiral vessels aro a quantity of solid strings coiled 

 #cIs> up into a spiral form. I cannot but suppose them of a lea- 



therlike substance, and to be found rolled round the last 

 few rows of sap vessels. In this manner they run up the 

 stems of trees and plants of every kind (with a few excep- 

 tions) and thence into every leaf and flower. They are 

 singly too small for the naked eye; they run into every fibre 

 of the leaf, and are fastened at the edges, by which means, 

 crossing like a spider's web in every direction through the 

 Tessels, they can draw the leaves in any way that is neces- 

 sary to them. In the larger vessels they are in sets of ten 

 or twelve, but in the smaller only three or four to each ves- 

 sel. In the cabbage leaf and in the burdock they are in 

 bundles almost as thick as a packthread; but in smaller 

 leaves they are properly proportioned. The more sensitive 

 the leaf, the more they are coiled up. These are (I truly 

 believe) the cause. 



The cause of The spiral vessels are ( I truly believe) the cause of mo- 

 motion in leaves ...» t j A t. ^ ^ 



and flowers. t ton in plants. 1 do not mean to say, that there is no mo- 

 tion in plants but what arises from them; but I am fully 

 persuaded, that the greatest part of the motion in leaves 

 and flowers proceeds from the management of this spiral 

 wire. I shall now detail my reasons for this persuasion. 

 Spiral vessels 1st. The spiral vessels are not to be found in any plants, 



leaves dut do to wn,fn mot " lon is unnecessary. They are never found in 

 not turn. any of the firs, in any of the water plants that spread their 



leaves on the top of the water, in any of the sea weeds, or 

 in any of the lichens; I think too they are not found in the 

 scolopendrums, or in the lemnas; though at first I took 

 the line of life, that runs into the leaf to form the flower, 

 for one. The grasses also, having no cause for turning 

 their leaves, are wholly without them. 



<id. If a plant in a window, having all its leaves with 



their backs turned from the light, is moved, and placed so 



a* to turn them to the sun, they will in a few hours regain 



> their 



