136 LEIPNER, ON SILICA IN PLANTS. 



formed by a transparent membrane^ composed of pure 

 cellulose^ an unazotized substance of 2 (C,^ Hjo Oj^) + HO. 

 This membrane is permeable by fluids, not by means of pores, 

 but by the process of endosmose. The interior is occupied 

 with mucilaginous matter, the " protoplasm" of Mohl, which 

 is at first homogeneous, but assumes by degrees a granular 

 appearance, and forms ultimately a layer on the inner 

 surface of the original cell, denominated by Mirbel and 

 others the " primordial or internal utricle." By successive 

 layers on the primordial utricle, the mucilaginous contents 

 of the cells form all the various secondary deposits, which are 

 frequ.ently arranged spirally ; but as this process of thicken- 

 ing by deposition advances, the original cell-Avall itself 

 becomes finally united with the secondary deposits. 



With regard now to the siliceous dejiosits in cells, it must 

 be remarked, in limine, that according to the opinion of all 

 physiologists the original cell-membrane is never composed 

 of anything but piu-e cellulose ; the silica must therefore 

 take, as it were, the place of the secondary cell-membrane 

 and cell-deposits. It is true, that by decarbonizing a sili- 

 ceous epidermis, either by chemical means or by burning, we 

 obtain a perfect membrane or tissue, in which the cells are 

 all attached to each other ; but this does not prove, that the 

 silica entered into the composition of the original cell-mem- 

 brane ; it merely proves that the secondary deposits have, 

 as 1 before stated, miited in their more advanced stage with 

 the primary cell-Avalls. That this is actually the case, my 

 own observations of the epidermis of canes and straw seem 

 to verify. For by continuing the action of chemical agents, 

 I have observed that the cells separated; from which I 

 have inferred that the cellulose membrane between the 

 individual cells, or in other words the primary cell-wall, had 

 been at length destroyed, which no doubt would have taken 

 place before, had it not been so intimately blended with the 

 secondary siliceous deposits. 



So far most physiologists I think pretty well agree ; but 

 when we come to inquire further : " What is the relative 

 position of silica and organic matter in the cells ? and what 

 is its mode of deposition ? " Ave meet either with very con- 

 flicting opinions, or Avith the most indefinite ideas. 



It thus happens, that though I have taken much pains to 

 consult the Avritiugs of such eminent botanists and physiolo- 

 gists as Lindley, Henfrcy, Balfovu-, Quekett, and my fellow- 

 countryman Schleiden, with others, I have not l^een able to 

 meet Avith even a clearly expressed theory upon this interest- 

 ing point. 



