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the bast fibres described by Krabbe, it can be proven that the 

 turgor cannot be raised sufficiently to produce this effect of 

 stretching, the only other explanation possible is that the walls 

 of the cells in question have undergone the following cycle of 

 changes : Their thin walls produced by the original division of 

 the cells composing them have been thickened so they have the 

 appearance as shown in fig. I ; then the matter composing these 

 walls has been partially absorbed till only the light wall remains 

 as seen in figure 2 ; this must also have increased in surface to 

 allow for the increased diameter as seen here. Then later on a 

 new process of thickening has taken place, by which the wall is 

 made much thicker then before. It must be noticed here that 

 there is not the same difficulty in the way of the wall stretching 

 out till the diameter required is reached as in the case described 

 by Krabbe. Here the young walls are in their early stage of 

 growth and there is every probability that a much smaller pres- 

 sure would serve to extend them than in case of the bast fibers 



of an older tissue. 



It is true that the simple fact that one explanation appears 



more plausible than another, is not at all of the nature of proof in 

 scientific research. At the same time the rapid succession of 

 changes noticed in the thickness of the walls of this tissue seems 

 worthy of record as a fact bearing on this subject. 



■ Another peculiarity still more striking than this occurs in the 

 course of the rapid growth and division of the epidermal cells be- 

 tween the wings. As before stated, these originate from a phel- 

 logcn layer extending not around the stem, but only for a short 

 distance around and beyond the little cluster of bast cells, the 

 wing shoving these out as it develops. In this variety the wing 

 never acquires a very great depth, but is of width enough to 

 materially aid in the enlargement of the circumference, while the 

 spaces between are thus enabled to assimilate. It is only, there- 

 fore, on the spaces between these wings that the epidermal cells 

 retain their character and divide, forming new ones. This pro- 

 cess does not result in the formation of corky layers, composing 

 the tissue known as periderm, but they form an additional sup- 

 port to the outer collcnchymatic cylinder, which at first is only 

 two layers in thickness. By means of these additional cells the 



