222 THE UNIVERSITY SCIENCE BULLETIN. 



the palisade tissue (fig. 2). The inner cell walls of the lower 

 epidermis are not as thick as those of the upper, and only a few 

 are mucilaginous. The mucilage may be so abundant, in varying 

 degrees, that the inner wall at first glance might seem to be a 

 second layer of epidermal cells, entirely filled with mucilage. 



The mucilaginous deposits probably serve as a place of storage 

 for water, absorbing a large amount when there is excess moisture 

 in the leaf, and then gradually giving this up to the palisade tis- 

 sue when the water supply runs low. I found no constant relation 

 between these cells having the mucilaginous inner wall and the 

 hairs, to indicate that water absorbed from the atmosphere by 

 the hairs would be delivered to them for storage. 



The midrib and the larger veins project prominently from the 

 lower surface of the leaf, and the greater portion of this projection 

 is composed of large thin-walled cells surrounding the vascular 

 bundle (fig. 13). Kuntze ('91) describes mesophyll cells on the 

 upper side of the vein, which break down to form large mucilage 

 channels in many of the Malvaceae. In the cross sections of the 

 veins examined no channels were found, and only a single cell 

 situated in this position showed mucilage (fig. 13, m). There are, 

 however, on the upper surface a large number of epidermal cells, 

 outlining the veins, which have a mucilaginous content (fig. 12). 

 Therefore we may conclude that mesophyll cells of the midrib, as 

 well as the mucilage cells, are good places for water storage, and 

 are probably used as such. 



The Stem. 



The stem structure follows closely the type form of the dicoty- 

 ledonous stem. The young stem is covered with both types of 

 clothing and glandular hairs described, under the leaf. These 

 hairs extend perpendicular to the surface, so that the young stem 

 looks quite fuzzy. The epidermis of the stem has regular cells, 

 the walls of which are not thickened to any great extent. The 

 cuticle on the outer wall is very thin, and I found no cutinized 

 layer which would aid in keeping in the water. 



The cortex is made up of four regions — an outer thin-walled 

 parenchyma, a collenchyma, a second thin-walled parenchyma, 

 and the starch sheath (fig. 15). The outer thin-walled parenchyma 

 is made up of three layers of radially enlongated cells. The col- 

 lenchyma tissue is composed of three layers, forming a broken 

 ring, with the gaps opposite the medullary rays. This arrange- 

 ment allows the water to pass in and out to the epidermis more 



