37 



parts, some hairs which are surrounded by an inflated, bladder- 

 like sac, often three or four times as wide, and twice as long as 

 the hair, very frequently much longer. The bladder commences 

 at the line of insertion of the hair on its pedicel (Figs. 12-14); "^ 

 fact, it is a film of cuticle continuous with the cuticle of the epi- 

 dermis, and raised from the cellulose body of the hair by a mass 

 of mucilage accumulating under it Chloriodide of zinc will 

 show that the wall of the hair inside the bladder really consists 

 of cellulose, while the membrane of the sac is stained bright yel- 

 low. This reaction will take place still more readily if applied 

 after short treatment with sulphuric or nitric acid. While examin- 

 ing the effect of these reagents, there will be noticed a great 

 many hairs, the sacs of which have burst at the top, after having 

 elongated often to five times the length of the hairs (Figs. 13, 17). 

 In other cases the entire sac has been torn off and carried away 

 by the increasing mass of mucilage, which is still kept together 

 by the thin but firm membrane of the sac. 



The mucilage itself is a viscid, coherent and very slippery sub- 

 stance. It is colorless but highly refractive, so that it can easily 

 be noticed around thin sections examined in water. It coagulates 

 in alcohol, boiling water will not dissolve it, but potassic hydrate, 

 sulphuric and nitric acids soon destroy it. Chloriodideof zinc gives 

 it a faint grayish color; potassic iodide and sulphuric acid color it 

 yellow. Nigrosin, an important reagent for vegetable mucilage, 

 stains it blue ; corallin slightly red, and osmic acid very light brown. 

 Hanstein's aniline and methylene blue color it red and blue, 

 respectively. But these aniHne dyes have a still more intense 

 effect on the numerous small and large fragrments of the sacs of 



£>^ ""*£> 



cuticle mixed with the mucilage, and also upon the countless 

 hosts of a peculiar kind of Bacteriiun, of the Bacillus form, that 

 are to be seen in every particle of mucilage. We might even be 

 led to consider this substance as the product of some zoogloea 

 form of Bacterium, if we had not watched the process by which 

 it is formed. 



Returning to the examination of the hairs that secrete the 

 mucilage, we select one of the very youngest, involute leaf buds, 

 a transverse section of which will exhibit all the stages of develop- 

 ment of the hctirs. Nearest to the margin of the leaf we discov^er 



