INTRODUCTION AND HISTORICAL BACKGROUND 7 



demonstrated what could be done with the polarizing microscope once 

 the underlying physical principles were fully appreciated. Careful 

 observations with this instrument convinced him that the building 

 material of 'starch grains, and subsequently of cell walls, was truly 

 crystalline; and later attempts to throw doubt on his interpretations at 

 the hands of Hofmeister and even of Strasburger were foredoomed to 

 failure. Following his studies of swelling reactions in starch grains, 

 Ndgeli concluded that they were composed of elongated particles lying 

 radially in the grain and separated by films of water. He deduced that 

 smaller particles should have thicker water films, and the famihar 

 lamellation was (again correctly) interpreted as due to alternation of 

 higher and lower water content. These elongated particles, which 

 Ndgeli later (1877) called micelles, were supposed to be stabilized in 

 these aggregates by the opposing attractions of the grains for each other 

 and for water. His greatest contribution at this time was, however, the 

 idea that starch grains increase in size by the insertion and growth of 

 new micelles between the old, and he soon extended this suggestion to 

 cover cell walls also. Such a process, which he called Intussusception, 

 fitted much more easily the conceptions of wall growth at that time than 

 did the apposition of von Mohl, and received general acclaim. As we 

 shall see later, it is amazing how near Ndgeli came to a description of 

 wall organization as we know it today. 



Not, however, that these ideas were accepted without some scepticism. 

 Strasburger' s denial of the existence of micelles and of any crystallinity, 

 coupled with his insistence on apposition, had the support of Noll, 

 Klebs, Zimmerman and Askenasy. On the other hand, a number of 

 investigators, notably Haberlandt, Zacharias, Krabbe and Cramer pro- 

 duced rather convincing evidence in favour of the ideas of Ndgeli. 

 Finally, Pfejfer in 1892 suggested that there might be no universally 

 acceptable mode of wall growth, and it goes without saying that later 

 work showed this to be the solution leading to the modern views which 

 will be discussed later in this book (p. W et seq.). 



During this time, parallel investigations had been going on in the 

 chemistry of the wall. As early as 1825 "cellulose" was known to be a 

 mixture of the substances cellulose and pectose. The first use of cupram- 

 monium to remove the cellulose was made by Fremy (1859) and the 

 subsequent staining and solubility tests soon led to the discovery that 

 the bulk of the pectic substances was located in the middle lamella 

 {Kabsch, Vogl, 1 863) though it must be remembered that at this time it 

 was not clear whether the middle lamella was a real cementing interstitial 

 layer or whether it consisted merely of the two primary walls. Sanio in 



