PIIYTOGENESIS. 25 1 



I return then to my question : what is the meaning of to 

 grow? In hackneyed phrase we are told, " To grow signift 

 increase of the mass of an individual, and takes place in the 

 inorganic world by juxtaposition, in the organic by intus- 

 susception." Have we gained anything for vegetable physi- 

 ology by this reply ? I think not. If the plant is to grow 

 by intussusception, then I say it consists of an aggregate of 

 single, independent, organic molecules, the cells j it increases 

 its mass by new cells being deposited upon those already ex- 

 isting i consequently by juxtaposition. But the single cell in 

 the progress of its expansion, which frequently reaches an 

 enormous bulk in comparison with its original size (I will 

 merely remind the reader of the pollen-tubes), also increases 

 in substance in the interior of its membrane, and by this 

 means also the mass of the entire plant is increased ; it con- 

 sequently grows by intussusception also. Finally, after a certain 

 period the cell deposits new organic material in layers upon its 

 primitive membrane ; thus another form of juxtaposition, which 

 still, however, belongs to the cycle of vegetable vitality. It 

 hence becomes readily apparent that, in respect to scientific 

 botany, the idea "grow" still requires a new foundation in 

 order to be capable of being applied with certainty. 



Of the three instances just cited, the second and third 

 belong more to the individual life of the cells, and are of 

 secondary importance only, as respects the idea of the whole 

 plant, regarded as an organism composed of a certain number of 

 cells. The plant considered in its totality increases its mass, that 

 is, the number of the cells composing it, in the first way only. 

 We must therefore here discriminate three processes essen- 

 tially distinct from each other in a physiological sense, which, 

 when strictly regarded, scarcely find an analogy in the other 

 kingdoms of nature. 



1. The plant grows, that is, it produces the number of cells 



allotted to it. 



2. The plant unfolds itself by the expansion and develop- 

 ment of the cells already formed. It is this phenomenon 

 especially, one altogether peculiar to plants, which, because it 

 depends upon the fact of their being composed of cells, can 

 never occur in any, not even the most remote form in crystals 

 or animals. 



