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A stratified wall consists of several layers which appear to be 

 quite distinct from each other when seen on the cross-section. 

 These layers often appear striated, or as havuig stripings running 

 more or less obliquely through them which on the cross-section 

 show like narrow lines. Krabbe used cross-sections of different 

 stems, IJnnm^ Urtica and others, and by an Ingenious method of 

 focushig by which the lines, according to their relative position 

 hi the layer, were made to recede from or approach each other, 

 claims to have proven that the process of intussusception could 

 not have taken place in the growth in thickness of the entire wall. 

 That is, he claims to have shown that the growth in thickness of 

 each one of these lamellae or layers was entirely separate from 

 that of the others, and that no interchange of micella; from one 

 layer to another could have taken place. 



The result of this study, ingenious as it was, led to no definite 

 results as to the actual manner of increase of thickness in a wall 

 already formed. Admitting that the two lamellae are entirely 

 independent of each other, each containing its own micella; from 

 the first, the question still remains, how did they reach their 

 present thickness ? He agrees with all the recent investigators on 

 this subject, that in many cases a so-called new formation of wall 

 occurs. To explain this we will suppose a cell with moderately 

 thickened walls; this when about to add to its thickness throws 

 out a new wall which eventually sets itself firmly on the old one 

 so as to become part and parcel of it. This building a new wall 

 by the protoplasm of an already enclosed cell is a process quite 

 lately discovered and in German Is known as *Mieubildung.'' 



In another portion of his work he claims to have reached more 

 satisfactory results; in fact to have actually proven that intussus- 

 ception does take place in the Increase of thickness In certain walls. 

 In certain plants of the families Asclepladaceae and Apocynaceae 



A 



there occurs a process of widening or bulging out of the walls ot 

 tlie bast cells in a very singular fashion, and afterward a cellulose 

 wall may be built across so as to form separate cells in the once 

 single bast fiber. Now as to the growth of these widcnings 

 it is plain that the number of micellae composing the growing 

 cell wall must have increased considerably. The question how 

 this increase is managed Krabbe answers by saying that it 



