296 DR. M. J. SCHLEIDEN ON PHYTOGENESIS. 



served in most of the plants which I have examined. There are 

 however several modifications of this process which add in many 

 parts to the difficulty of observation, nay sometimes render it 

 quite impossible, although notwithstanding this the law remains 

 in general indisputably valid, because the analogy requires it, 

 and moreover we can sufficiently account for the reasons of the 

 impossibility of direct observation. 



The difficulties which I here notice arise especially from the 

 physical and chemical properties of the substances preceding the 

 formation of cells. The above enumerated ingredients are to be 

 considered as scarcely anything else than some few points, which 

 for the purpose of giving a general view, and to render the clas- 

 sification more easy, I have intentionally selected from the or- 

 ganic chemical processes of vegetable life, which are constantly 

 in operation, and with which as yet we are entirely unacquainted. 

 Almost all those substances exist constantly together in the 

 living plant, and only their greater or less preponderance author- 

 izes the expression, that the cell contains amylum or gum, and 

 so forth. Towards the termination only of the individual life of 

 the single cells do we find them filled with a less number of dif- 

 ferent substances ; with one only, probably in those cells alone 

 which contain volatile oil. 



If now we suppose that the cell is entirely filled with a limpid 

 solution of sugar in which gum is rapidly generated, but only 

 just so much as is necessary to form, by as quick a conversion 

 into gelatine, a delicate cellular membrane, whose existence, in 

 consequence of a similar refracting power of the wall, of the con- 

 tents, and of the surrounding medium, we are not able to distin- 

 guish with the microscope; — then it becomes highly probable, that 

 a number of such formative processes may be going forward which 

 escape our observation, and become known to us only by their re- 

 sults, when we find, after the reabsorption of the primitive cell, two 

 new ones suddenly in its place. If on the contrary our attention 

 has been previously directed to this process, we have, it is true, 

 by employing reagents, especially iodine, which is quite indispen- 

 sable to the physiological botanist, several means at hand of ren- 

 dering it visible where such a formative process is suspected. Gra- 

 dual transitions to the perfectly invisible processes will be easily 

 found by extensive examinations : I will as an example just 

 mention one of the most difficult cases I have met with. This 

 occurs in the germination of the spores of Marchantia poly- 



