174 HISTORY OF BOTANY 



chemistry of the cell wall ; and (4) the protoplasmic 

 inter-relationship of cells. 



Following on the generalisation we now know as the 

 " cell theory," a considerable amount of work was carried 

 out on the differentiation of permanent tissues from 

 primary and secondary meristem on the lines laid down 

 by Hanstein in 1868, and with these investigations we 

 must associate the names of Sachs, De Bary, Van Tieghem, 

 Jeffrey, and Haberlandt. The mechanical tissues and 

 their arrangement in the different organs of the plant 

 were worked out by Schwendener in 1874, while numerous 

 papers were also published on points of detail or on the 

 anatomy of special plant types. Let us look at some of 

 this work a little more closely, beginning with the problems 

 concerned with the cell. 



Protoplasm was described by Max Schultze, Von 

 Mohl, and others as a colourless, viscid, granular substance 

 lining the wall, or more or less filling the cavity, of the 

 cell, and exhibiting streaming movements or cyclosis 

 when free to move as in the case of the Mycetozoa. 

 By 1875 it was generally accepted that protoplasm 

 consisted of a framework or reticulum of delicate fibrillae, 

 whose meshes were filled with a fluid " enchylema," the 

 nodes on the reticulum giving the appearance of granula- 

 tion. The most important modification of this view was 

 that advanced by Biitschli in 1889, and known as the 

 " foam theory/' According to Biitschli the protoplasm 

 is to be likened to a froth made by rubbing up oil with 

 a solution of potash or cane sugar, which, under the 

 microscope, presents the appearance of a network, the 

 threads being the optical sections of the walls of the 

 droplets. In this foam numerous granules are suspended, 

 especially at the angles where the droplets touch each 

 other. The free surfaces of protoplasm were observed 

 to be of a denser consistence than the remainder, and 

 were distinguished by Hanstein as composed of 

 " ectoplasm " in contrast with the inner more granular 



