ORGANIZED BODIES. 205 



great amount of cell matter is formed, which appears to be deposited between the bark and 

 wood ; this cell matter, called by some cambium, is derived from the inner cells of the bark 

 and the outer cells of the wood ; it is really a multiplication of cells, from the bottom of the 

 tree to its top, a simultaneous production of new cells throughout the whole extent of the sur- 

 faces concerned. In time this pulpy matter, which consists of immature cells, becomes ligni- 

 fied and hard. It is not a slow development of cells proceeding from above downward ; it is 

 a cell growth, having its power seated entirely in the preexisting cells. The bark produces its 

 own peculiar cell, and the wood its own ; for the character or structure of the bark cell is un- 

 like that of the wood cell. The sap, flowing down between the bark and wood, has no power 

 in itself to produce cells ; it would be merely extraneous matter : it is only by cell power 

 that new cells or growth is effected. The doctrine that there is usually a downward circula- 

 tion seems unnecessary : that fluids may take this direction, under certain conditions, is pro- 

 bably true ; and I do not deem it an established fact that the movement of sap is entirely due 

 jo the leaves, inasmuch as the sap ascends before the leaves are developed, and also in that 

 peculiar process already alluded to in overgrowth. In these two facts we are driven to ac- 

 knowledge in growth a cell power ; but we are not driven to the necessity of admitting that 

 exhalation, in either of these cases, is wanting. In organized bodies, production presupposes 

 a producing organ : it produces its like — it multiplies its identical self and nothing else. We 

 could have no certainty that an extraneous, unorganized fluid, though circulating within the 

 pale of a vegetable, would produce the identical cell of the vegetable ; a special organ only 

 can do this. 



On the conveyance of food through the root and all parts of a plant, Mulder makes the fol- 

 lowing remarks :* the substances existing in the soil, in the state of liquids, are absorbed by the 

 roots, by endosmotic action ; that is, the cells of the fibrils are filled with one liquid, and are 

 surrounded by another, which is present in the soil. The latter fluid is less saturated than the 

 former, and hence it penetrates through the cell walls of the epidermis of the fibrils, in the 

 ▼cry young cells especially, where the fluids become diluted. From these cells the liquid en- 

 ters the adjacent ones, and so on, till it traverses the whole plant If we commence with the 

 leaves and proceed downward, we find first, that on their surfaces evaporation takes place j 

 the liquid becomes more concentrated thereby, but this will be diluted endosmotically by the 

 thinner liquid which exists in the neighborhood j this thinner liquid exists in the adjoining 

 cells below, and thus the most dilute and thinnest of all is found in the fibrils of the root ; and 

 in the soil surrounding the roots it is still more dilute. The connection is therefore very close, 

 according to Mulder, between the absorption of the saps from the soil through the root, and 

 their ascent into the plant ; both being ascribed to one cause. 



The inference is then drawn, that growth, the ascent and the absorption of nutritive matttf 

 from the soil, depend on the evaporation from the leaves. The solutions of matter which are 

 taken up by the roots are extremely dilute ; even many coloring matters will scarlely pass 



* See p. 621, Miju)ek'8 Chemistry of Pbysiologr. 



