THE CELL-MEMBRANE. 353 



difference, though he admitted it in certain cases, but even 

 then he did not hold that it proceeded from any metamor- 

 phosis of the membrane which took place gradually at the 

 periphery of the cell-walls. 



The vnew that such chemical difference does exist and 

 that the opinions of the earlier workers in this field are in 

 the main accurate, receives some support from Van Tieg- 

 hem's observations on the progress of putrefaction set up 

 by bacteria. In his Traitii de Botanique {21) he shows that 

 Bacillus Amylobactcr disintegrates vegetable tissues by dis- 

 solving the middle lamella. He says that the cellulose of 

 the wall exists in two varieties, one of which is split up by 

 the micro-organism into butyric acid, carbonic dioxide and 

 hydrogen, while the other is unaffected. As Van Tieghem 

 gives no reactions which are distinctive of these two varie- 

 ties, it is clearly open to us to hold the view which accords 

 with earlier investigations, namely, that the material dis- 

 solved by the bacterium is pectic in its nature and that pure 

 cellulose is unaffected by it. 



Besides the middle lamella, other modifications of the 

 original w^all need mention. Chief among these we have 

 the so-called intercellular protoplasm of Russow (2). He 

 described this substance as forming in certain cases a deli- 

 cate membrane or lining -layer, coating the intercellular 

 passages. This substance has been critically examined by 

 Gardiner and by Schenck, both of whom deny its proto- 

 plasmic nature. Gardiner (3), relying on certain staining 

 reagents, especially methylene blue, advanced the view that 

 it is a product of cellulose decomposition, probably a kind of 

 mucilage, and states that it varies very much in composi- 

 tion in different cases. Schenck held that it is of the same 

 general nature as the middle lamella, but declined to give a 

 more definite opinion as to its nature. Mangin considers it 

 to be composed of a mixture of pectic bodies. 



The rod-shaped filaments and concretions of various 

 shapes which are found in the intercellular spaces of many 

 of the Pteridophytes and in the integuments of the seeds of 

 some of the Papilionaceae have also been variously stated to 

 be protoplasmic or to be formed of cutinised material. 



24 



