218 PROTOPLASM. 



from the cells around the buds which form on the incised leaves 

 of Begonia. 1 



594. The relations of the cell- wall to protoplasm are not yet 



fully understood ; and in regard to some of them there exists 

 among botanists considerable diversity of opinion. The two 

 principal views are the following: 1. The cell- wall is formed 

 by the solidification upon the exterior of a protoplasmic mass, 

 of matters previously dissolved in it. The pellicle thus pro- 

 duced is regarded as a sort of excretion (since in most cases it 

 is not again to be dissolved and employed by the organism) or 

 as a secretion (because in a few instances it can be dissolved 

 and utilized a second time by the plant). The substance capa- 

 ble of thus solidifying upon the surface of protoplasm consists of 

 cellulose combined with water and a small amount of incombus- 

 tible matters, but it is not positively known in what condition 

 these were previously combined in the protoplasm. 2. The 

 cell-wall may be regarded as directly produced by a conversion 

 of the outer film of protoplasm into cellulose with which some 

 other matters are intermingled.' 2 



595. The young cell-wall 3 is practically a homogeneous film of 

 cellulose, which speedily undergoes changes both in its chemical 

 and physical character. In man}' of the lower plants the wall 

 differs in some particulars from that found in the higher plants 

 (see p. 29), but the differences need not enter into the present 

 description. 



596. Two views are held respecting the mode of growth of 

 the cell- wall. The first may be regarded as based upon the 

 Irypothesis of Nageli spoken of in 588. From some of the mate- 

 rials held dissolved in the adherent film of water around each 

 micella new micellae of cellulose are supposed to be produced, 



1 "That protoplasm can pass through closed cell- walls is beyond doubt " 

 (Vines, note to second edition of Sachs's Text-book, p. 946). 



2 The view that cellulose is a kind of secretion is stated at great length in 

 Hofmeister's Pflanzenzelle, and in several communications by Sachs in Bota- 

 nische Zeitung. The second view is given by Schmitz, Sitz. der niederrhei- 

 nischen Gesellschaft fur Natur- und Heilkunde, Bonn, 1880. He bases his 

 opinion largely upon the fact that in some cases the cells gradually become 

 emptied of protoplasm as the amount of cell-wall increases, and upon the phe- 

 nomena which attend the increase of the cell-wall in thickness. 



3 It was believed by some of the earlier phytotomists that the cell-wall was 

 a close, firm network of extremely fine fibres, while others held it to be com- 

 posed of minute granules. In these explanations of structure it was confessed 

 that the ultimate fibres, or ultimate granules, lie quite beyond the reach of the 

 highest powers of the microscope. 



