OF THE ELEMENTARY STErCTrKES. 739 



culation in Vallisncria, as seen when magnified 2,800 diameters 

 {How to Work zvith the Microscope, plate 38, fig. 2i4) ; he 

 describes the circulating stream as consisting of extremely 

 minute apparently spherical particles of "germinal matter . . . 

 endowed with active motive power," and with them the larger 

 masses of chlorophyll are carried on. In the Characece, and 

 especially in the XitcUce, which are transparent, the moving pro- 

 toplasm does not rotate round the walls, or in reticular currents, 

 but it passes obliquely up one side of the cell (/y. 1095) until 

 it reaches the extremity, and then flows down in an opposite 

 direction on the other side. 



No satisfactory explanation has as yet been brought forward 

 to account for this movement ; all that we know is, that it is 

 connected with the vitality of the cell-contents, and that all 

 agents that actually injure the cell will stop it at once and per- 

 manently. The movements of the ciliated zoospores of the 

 Algffi (see p. 381, and fffi. 30-32 and 832); and those of the 

 ciliated spermatozoids of Algse (see p. 385 and fig. 841), and 

 of the higher Cryptogamic plants (see p. 361 and/^. 788), are 

 regarded by Henfrey and others as " analogous to the rotation 

 of tJie protoplasm." 



4r. Elaboration of the Cell contents. — All cells exposed to light 

 and air which contain a primordial utricle, have the power of 

 producing in their contents the various azotised and unazotised 

 compounds which are concerned in the development of new 

 tissues, and in the formation of the various secretions of the 

 plant. (See Respiration and Assiiuilation.) In old cells the 

 secretions of the plant are also, in part, deposited. 



2. FrxcTioxs OF PEOSEXCHTMATors Cfxls a>t) Peosex- 

 CHYMA. — Prosench}Tnatous cells are especially adapted by their 

 construction and mode of combination into a tissue, for giving 

 strength and support to plants ; and there can be no doubt, but 

 that this is one of the offices which they perform. In a young 

 state, also, before such cells are filled with secondary deposits, 

 they appear to be the main agents, by which the fluids absorbed 

 by the roots are carried upwards to the leaves and other ex- 

 ternal organs, to be elaborated by the agency of light and air. 

 The experiments of Hoffman, Unger, and others, seem to prove 

 this. Thus, Hoffman, by placing plants in such a situation as 

 to cause them to absorb a solution of ferrocyanide of potassium, 

 and then adding a persalt of iron to sections of them, found that 

 the Prussian blue which was formed by the reaction of the 

 chemical agents thus applied, was principally deposited in the 

 prosenchymatous cells. Unger also came to the same conclusion, 

 by causing plants to absorb a coloured vegetable juice, ancl 

 tracing its passage. It should be noticed, however, that other 

 experimenters, such as Link, Eominger, and Spencer, have 

 arrived at opposite conclusions. (See Functions of Vessels.) 



