HISTOLOGY OF STEM OF THE WAX PLANT 269 



the figure obtained by calculation (.03 mm.) without serious error. 

 Making the same calculation for a girdle 3 mm. in diameter where the 

 cells were 220 in number, we find their diameter to be .04 mm., while 

 their measured diameter is .05 mm., the difference being doubtless 

 due to the overlapping of the cells. 



Calculation ^^ — = — — ^ = .035 mm. 



20.9 209 



Hence we see that the elongation of the cell is sufficient to account 

 for the increase of the girdle thus far. But when we look at a section 

 in which the sclerotic ring measures 7 or 8 mm. in diameter, we see 

 that it contains many small round cells as well as the flattened ones, 

 and in some places the girdle is separated by a cell of parenchyma, 

 thus suggesting that the increeise in growth is not due to the compres- 

 sion of the cells alone, but that some of them separate, and the spaces 

 left vacant are filled by parenchyma that soon becomes lignified. This 

 must talce place very rapidly, as I have never found sclerotic cells in 

 the process of formation in the girdle of the older portions of the stem. 



As stated before, the object of the sclerotic girdle is probably the 

 support of the young stem, as the plant twines but feebly. When the 

 stem reaches a diameter of ten or twelve millimeters, the girdle no 

 longer stands out as a conspicuous component of the section, but is 

 separated in places and appears to be gradually losing its identity, and 

 I venture to say, if its object is as I have supposed, that in a still larger 

 stem the girdle, being no longer needed for support, would be foimd 

 disintegrated and mingled with the sclerotic cells of the parenchyma. 



The Inner Band of Parenchyma 



This is composed of cells similar in structure, shape, and size to 

 those of the outer band, and also contains besides the bast fibers, 

 sclerotic cells, chlorophyll, crystals, and starch. It is the outer cells 

 of this band that are filled with starch before the development of the 

 sclerotic girdle. The bast fibers lie scattered in bimdles mostly near 

 the outer boundary of the band. They are fusiform in shape, about 

 20 /A in diameter, their walls are about 6 m in thickness, and are very 

 faintly marked in the manner shown on pi. II, fig. 8. 



It is very difficult to determine their average length. None of 

 those I have been able to isolate with certainty have measured over 



