CHAP, i The Cell 183 



and far too small to be visible under the microscope. Each 

 is surrounded by a layer of water, so that adjacent particles 

 are not in direct contact. They may be of different sizes, 

 and the watery layers between them may be of varying 

 thickness, so that the density of the structure will depend 

 on the relative amounts of the solid and liquid constituents. 

 The wall is the scene of action of two forces, the particles 

 being mutually attractive, and the water forcing them 

 apart as more is absorbed by the wall under external 

 pressure, or as it is attracted by the surfaces of the particles 

 owing to surface tension. The particles may be arranged 

 in layers of different degrees of density, watery and more 

 solid laminae alternating. Growth in surface or in thick- 

 ness depends on the intercalation of new particles among 

 those already existing. 



This hypothesis gave what appeared to be a satisfactory 

 explanation of all the facts that had been observed up to 

 that time. It is not surprising, therefore, to find that it 

 met with a very cordial welcome. Sachs spoke of it as 

 ' the first successful attempt to apply mechanico-physical 

 considerations to the explanation of the phenomena of 

 organic life '- 1 



After about twenty years of supremacy Naegeli's hypo- 

 thesis was challenged by Schmitz and especially by Stras- 

 burger, the latter of whom put forward a view which, 

 while admitting the cell wall to be composed of solid and 

 liquid constituents, opposed the theory that the former 

 are crystalline. The existence of the micellae, as Naegeli 

 called the crystalline particles in 1877, was altogether 

 a matter of inference, as they were supposed to be far 

 too minute for microscopic demonstration. Strasburger 

 eliminated them entirely from his conception. He held 

 that the forces binding together the solid particles are 

 rather chemical than physical ; that their molecules are 



1 History of Botany , Eng. ed., p. 315. 



