THE ACHROMATIC FIGURE, CYTOKINESIS, AND CELL WALL 193 



that the wall is made up of ultramicroscopic crystalline micellae, sur- 

 rounded by water films. Growth of the wall in thickness and in area he 

 believed to be due to the intercalation of new micellae between the old ones, 

 a process termed intussusception. Contrasted with this was Strasburger's 

 development of the apposition theory (1882, 1889). Although Stras- 

 burger agreed that the wall had both solid and liquid constituents, he 

 held that the latter were not complex micellae, but only molecules linked 

 together in the form of a reticular framework by their chemical affinities. 

 Growth in area he thought was merely a matter of stretching without the 

 intercalation of additional particles, while increase in thickness was 

 supposed to be accomplished by apposition, or the deposition of layers 

 of new material in the form of small particles, or microsomes. The 

 striations which both he and von Mohl observed in the wall substance 

 were regarded by Strasburger as due to the linear arrangement of these 

 microsomes. 



That the cell wall is not merely a lifeless secretion of the protoplast, 

 but contains protoplasm in some form, is a view which has often been 

 upheld, and involves problems which are still far from being solved. 

 Prominence was given to the view by Wiesner (1886), who looked upon 

 the growing cell membrane as a living part of the cell. Following Stras- 

 burger's early view, he held the primary layer- to be wholly protoplasmic, 

 and supposed the growing wall to be made up of regularly arranged 

 particles, which he called dermatosomes, connected by fine fibrils of 

 protoplasm. Growth was accomplished by the intussusception of new 

 dermatosomes. Evidence in support of Wiesner's interpretation was 

 brought forward by Molisch (1888), who showed that when tyloses come 

 into contact pits are formed exactly opposite each other in the two 

 abutting walls, a phenomenon which it would be difficult to explain were 

 the walls without living substance. 



The new intussusception theory of Wiesner was accepted by a number 

 of workers including Haberlandt and Zacharias (1891). The apposition, 

 or lamination, theory of Strasburger also had many supporters, among 

 them being Noll (1887), Klebs (1886), Zimmermann (1887), and Askenasy 

 (1890). According to Pfeffer (1892) both processes, the intussusception 

 of new particles or molecules and the apposition of new material in layers, 

 are concerned in the development of the wall. This view was later 

 adopted by Strasburger (1898), and has received general acceptance. 

 But much work must be done before any final conclusion can be drawn re- 

 garding many points. Especially obscure is the exact relationship of 

 the protoplasm and the wall. The solution of this difficult problem 

 must await the results of further inquiries by both the cytologist and the 

 biochemist. 



The Chemical Nature of the Cell Wall. Through the researches of 

 Payen (1842), Fre"my (1859), Kabsch (1863), Wiesner (1864, 1878), and 



13 



