96 ORGANS AND FUNCTIONS OF PLANTS. 



heat is greatest, the rise of the sap is most rapid, 

 there being a stop, if not a retrograde movement, 

 during the night. Cloudy weather will also diminish 

 the ascent, and a gleam of sunshine increase it, on a 

 principle to he immediately explained. 



Experiments and Researches on Circulation. 



M. Corti, in 1775, discovered by means of the mi- 

 croscope, a movement in the fluids of stonewort ' which 

 the Abbe Fontana considered to be a species of rota- 

 tion. The appearance has again been brought into 

 prominent notice, in 1823, by Schultz and Amici; 

 in 1827 by Meyer; and in 1831 by Dutrochet, Mirbel, 

 and others, who have observed this rotatory movement 

 in water plants, whose textures are transparent, and in 

 land plants with milky juices. 



In stonewort and other water plants, the fluids are 

 seen to contain small solid floating particles, usually of 

 a vivid green colour, which are seen to rise till they ar- 

 rive at a horizontal partition, when they take a horizontal 

 course to the opposite side, and there descend perpen- 

 dicularly to the bottom of the cell in which they may 

 be, and then cross horizontally to the place whence 

 they started. .There are always, of course, motions in 

 four directions ; and, what is singular, the motions in 

 each vessel seem independent of those in all the other 

 vessels, and the moving globules are never seen to pass 

 from one to another, there being indeed no outlet for 

 their passage. 



The greater celandine, which has thick yellow juice, 



(1) In Latin, Chara saxatilis. 



