192 The Anatomy of Plants BOOK n 



The first formation of the cell wall observed to take place 

 over the surface of naked masses of protoplasm was attri- 

 buted by von Mohl and by Naegeli to a process of secretion 

 by the outer layer. Strasburger's observations appeared 

 to be at variance with this view, for he interpreted them 

 to mean the conversion of protoplasm into cell-wall sub- 

 stance. It was not till 1898 that the two theories were 

 reconciled, when he formed the opinion that the cell plate 

 first formed from the microsomata splits into two laminae, 

 between which the true cell wall appears as a secretion 

 product. 



The chemical character of the cell wall was studied by 

 many workers after the appearance of Mangin's memoirs. 

 Tollens investigated the pectosic compounds in 1895 in 

 connexion with his work on the carbohydrates in general, 

 and determined many points of their relationship with 

 different kinds of sugar. E. Schulze in the previous year 

 greatly extended our knowledge of the celluloses. 



The varied character of the cell wall was pointed out by 

 De Bary in 1884, when he showed that the membranes of 

 fungi do not give a blue coloration with iodine and 

 sulphuric acid. This so-called fungus-cellulose was proved 

 to consist very largely of chitin by Van Wisselingh in 1898, 

 a discovery led up to by the observations about four years 

 earlier of Winterstein, Gilson, and other writers, that 

 chitin and cellulose are associated in various animals, while 

 cellulose itself is present in the Tunicata. Van Wisselingh 

 proved the presence of chitin in the cell walls of several 

 species of fungi by heating to 160 C. in concentrated 

 caustic potash solution for two hours, material that had 

 been preserved in alcohol, and subsequently washing it 

 with strong spirit and staining it with iodine and sulphuric 

 acid. Chitin under such treatment becomes pink, whereas 

 cellulose turns blue. 



The laws governing cell divisions and the formation of 



