266 HISTOLOGY OF STEM OF THE WAX PLANT 



found outside of the sclerotic girdle more frequently than the above 

 statement would seem to imply. They are filled with a greenish 

 yellow fluid distinctly granular in structure. They can be very readily 

 seen in a longitudinal radial section and also in a tangential one that 

 passes through the parenchyma of the bark. 



Chlorophyll 



The chlorophyll is principally contained in the outer border of the 

 parenchyma and is composed of granules about 5 At in diameter. I 

 have been unable to decide whether they contain starch, but think 

 that they do. The inner band of parenchyma also contains chloro- 

 phyll on its outer boundary, but it is not found in any other parts of 

 the stem, to my knowledge. 



Starch 



In the outer band of parenchyma starch is very abundant and 

 completely fills some of the cells. The granules vary in size, but 5 ^l 

 would perhaps be a fair average. They do not show any markings as 

 far as I have been able to observe, except a slight suggestion of a 

 granular structure. In this band of tissue starch also occurs in the 

 inner ring of parenchyma, in the wood, pith, and medullary rays, if 

 what I consider the latter proves to be correct. The occurrence of 

 starch varies with the treatment the plant has received, for on making 

 a' section of a plant that had been for some time without water, the 

 starch had almost entirely left the parts of stem where it was abundant 

 before. In regard to the protoplasm I can only say that it is contained 

 in the cells of this band, but I have not attempted to investigate its 

 properties, as the object of this paper is to describe the structure of 

 the plant cells rather than their contents. 



Sclerotic Cells 



These will be considered when treating the sclerotic girdle. It is 

 only necessary to state here that they occur in abundance just under 

 the bark and are irregularly scattered through the band of parenchyma. 

 They increase in number as the plant grows older, and it is in the old- 

 est portions of the stem that we find them most numerous. 



This plant offers better opportunities for the study of these cells 

 than any known to me. They are to be found in the petiole and leaf 



