214 LINK ON CELLULAR TISSUE. 



net-work, of which the meshes are the cells. It is very probable that 

 Hedwig, who has written much on the theory of the mosses, has suf- 

 fered himself to be deceived by this same net-work, so as to believe it 

 constitutes a separate species of vessels, w hich he called vasa reve* 

 hentia. Such a net- work occurs in the scales (strigce) of the Sco- 

 lopendrium vulgare, and is remarkable because the intervals are of 

 a different colour from those of the cells ; and they furnish an un- 

 doubted proof of the existence of the intervals. 



M. Mirbel compares the tissue of cells to froth produced by soap 

 and water. This comparison is very exact. I do not know a better. 

 But the author entirely forgets the double partitions, which do not agree 

 with this comparison ; for the froth of soap is composed of bubbles 

 of air, separated originally from each other, so that each bubble is 

 formed, as it were, of a separate membrane ; and it is only by ap- 

 proaching, that these partitions are confounded together. It often 

 happens that single bubbles rise to the surface of the froth, as we see 

 single cells in the cavities of the stalks in the receptacle of flowers or 

 of fruit. I even think that the cells have had the same origin as the 

 bubbles : gas having developed itself in a viscous fluid, and reduced it 

 to little vesicles, which have united together. As the vesicles of the 

 tissue of cells have a more regular arrangement than soap bubbles, a 

 particular attraction, necessary for the growth of the vegetable, must 

 have set them in that order. According to M. Sprengel, the tissue of 

 cells derives its origin from small grains, which are found in the cells 

 of the seed, and several other parts. I have proved that these little 

 bodies are usually grains of starch, sometimes grains of mucilage. 

 They may be dissolved in warm water, and sometimes in cold, while 

 on the contrary, the membrane resists all these solvents. It is there- 

 fore certain that these little grains are not cells. But it is very pos- 

 sible that these grains may be dissolved in the sap j and that they 

 then form that viscous fluid, which gives rise to the production of new 

 cells. 



The cell appears to be perfectly closed, so that the sap, which 

 doubtless passes through the tissue of cells, penetrates by impercepti- 

 ble pores. There are examples, in which we distinctly see the juice 

 pass through this kind of pore. If the flower cup of the lettuce be 

 pressed ever so little, a small drop of milky fluid appears through the 

 rind, where no pores are discernible, even with the aid of the most 

 powerful microsqope. M. Mirbel has, however, found pores, sur- 



