THE VEGETABLE CELL. 61 



II. THE PHYSIOLOGICAL CONDITIONS 

 OF THE CELL. 



Even as in anatomical respects the cell appears, on tlie one hand 

 as an independent organism, self-contained, and following its own 

 proper laws of formation in its development, and again, on the 

 other hand, in the great majority of plants, does not appear iso- 

 lated, but forming part of a greater whole, with which it is not 

 merely mechanically connected, but by the influence of which its 

 organic development is modified, so that its form, the position of 

 its pits, &c., are dependant on the condition of the neighbouring 

 cells, — so, in like manner, is the physiological activity of the cell, 

 on one hand independent of, and on the other dependant on, and 

 ruled by, the vital activity of the entire plant. 



The vital functions of plants are separable into two great 

 classes, into those of nutrition and those of propagation. Both 

 are committed to the cells. The share which the individual cell 

 takes in one or both of these functions varies extremely according 

 to the degree of elevation of the organization of the plant. 



In the lowest plants, whether, as in Protococcws^ they consist 

 of a single cell, or as in the Confervas of rows of cells united into 

 a thread, each cell is capable of an independent existence. It ab- 

 sorbs fluid from the surrounding medium, respires, assimilates the 

 absorbed substances, &c. ; in short, the simple vesicle suffices for 

 the accomplishment of all the various functions which must co- 

 operate in the nutritive processes of the plant. The more highly 

 organized a plant is, the more these various functions are com- 

 mitted to particular organs, the offices of which in this way be- 

 come special and one-sided, thus being reduced to a dependance 

 on the functions of the other organs. The function of absorption 

 is committed to the root ; that of breathing and the elaboration of 

 the absorbed substances to the cells of the leaf, &c. With the 

 combination of many cells into a whole, leading a common life, 

 comes the necessity of a passage of the sap from one organ to 

 another, a circulation of the fluids, which the simply formed plant 

 can wholly dispense with. This movement of the sap is in great 

 part committed to particular cells, which take but a subordinate 

 part in the real business of nutrition. 



Analogous to the more independent condition of the ceU. as an 

 organ of nutrition, in proportion as the organization of a plant is 

 simpler, the greater is its activity as an organ of propagation. In 

 the lowest plants the same cell is an organ of vegetation in the 

 earlier period, and an organ of fructification in the later period of 

 its life, germinal granules (keim-kdmer) being formed in its in- 

 terior. In the higher plants, on the contrary, these two functions 

 are committed to different cells, in which case, at first, as in the 



