DALBEY: ANATOMY OF GRINDELIA. 35 



per cent of the surface area is covered by these droplets, and on 

 the lower surface 2.6 per cent. This gum-resin has a composite 

 character. It swells and is slightly soluble in water, the solu- 

 tion showing an acid reaction. When a dry leaf was put into 

 hot water and left for twenty-four hours the gum disappeared 

 from the surface of the leaf, and that on the margin became 

 viscous. Some of this gum-resin from the margin, after soak- 

 ing in water twenty-four hours, was put in ether ten minutes, 

 but did not dissolve. It is partially soluble in ether, alcohol and 

 xylene, and when a small amount, placed on a slide, was irri- 

 gated with ether for a period of about ten minutes, a part dis- 

 solved, and the residue gave the reaction for gum when treated 

 with methylene blue. 



The substance shows the characteristic red stain when left 

 twenty-four hours in a solution of alcanin, or in Sudan III, 

 but it failed to show a resin reaction with copper acetate. 



It may be possible that the tracheids at the margin of the leaf 

 (fig. 13) function as water-storage cells, the resin serving to 

 prevent transpiration in time of drouth ; however, this is not a 

 very satisfactory explanation of the relationship of the glands 

 on the surface to the conducting and water-storage systems of 

 the leaf. (Figs. 3, k, and 14.) It seems more probable that 

 these glands function as organs of absorption. Kerner and 

 Oliver (10) cite the case of an Aizoon having epidermal glands 

 which serve to collect water and transfer it to the cells within 

 the leaf. The gum resin, which swells in water, may be able to 

 absorb the water from the rain and dew and transfer it, by 

 osmosis, into the cells of the glands, whence it might pass into 

 the noncutinizecl elongated cells of the epidermis and on into 

 the adjoining water-storage tracheids (fig. 13), or into the 

 water-storage cells of the mesophyll (figs. 3, k, and 11, u) , and 

 from these storage cells it could be slowly given off to the plant 

 in time of drouth. 



THE STEM. 



The stem has a gray-green color, with a minutely roughish 

 surface. In cross section it is round, with the outline broken 

 by from three to eight protuberances, which occur at regular 

 intervals. (Fig. 25.) Glands similar to those found on the 

 leaf are distributed irregularly over the surface of the stem. 

 The cross section shows a circle of open collateral bundles vary- 

 ing from ten to thirty-four in different sections. The stem is 



