17 BOTANICAL MICROTECHNIQUE. 



membranes. Klebs used in these studies a .01$ solution of 

 Congo red or a suitable culture fluid to which the same pro- 

 portion of the dye (i : 10,000) was added. But it should be 

 observed that the Congo red deposited in the membranes 

 strongly hindered their superficial growth in Klebs' experi- 

 ments, while their growth in thickness was so much the 

 more increased, and the vitality of the cells was in no wise 

 destroyed. 



ii. The Finer Structure of Cell-walls. 



2p7f. Many cell-membranes, especially those of consider- 

 able thickness, are well known to be made up of various 

 lamellae or layers parallel to their surfaces (stratification). 

 In many there occur band-like differentiations within the 

 same layer, which, according to Correns (III, 324), always 

 have a spiral course (striatiori). Finally, one finds not 

 uncommonly radially arranged lamellae of varying optical 

 properties (transverse lamellatioit). 



The observation of these differentiations may in many 

 cases be conducted on the unchanged membranes. But in 

 general they come out much more plainly if the membranes 

 are treated with swelling media ; and, besides those men- 

 tioned in 10, chloroiodide of zinc is in many cases very 

 useful, 



2p7g. Three factors may enter into the problem of the 

 cause of the optical appearances described, which have been 

 thoroughly discussed by Correns (III): I. Sculpturing of 

 the wall ; II. Differentiation of the wall into strips or layers 

 of unequal water-content with similar chemical constitution ; 

 and III. Differentiations of the wall which possess, with 

 similar water-content, unequal refractive power, and there- 

 fore depend upon material differences. Besides these, only 

 combinations of these three factors are possible. 



2Q7h. Sculpturing of the wall may produce especially stri- 

 ation. This then falls into the category of partial thicken- 

 ings of the membrane, and deserves to be considered here 

 only because, when very delicate, it cannot be distinguished 



