191«I Hall-Goodspeed: Chrysil 218 



excess was washed from the sections with 50 per cent alcohol. The 

 sections were then monnted in glycerine and in some cases were ringed. 



Some search has been made for a staining method which would be 

 strictly definitive for rubber and which would result in imparting 

 such a chai-aetei'istic color to the rubber cell-inclusions as would serve 

 to distinguisli them definitely from all other inclusions. The desira- 

 bility of securing such a staining method is seen in tlie fact noted 

 above, that alkanin and Sudan III are in histological practice used to 

 indicate the presence of resins and fats, respectively, and thus their 

 ability to stain rubbei' in the cell is in a sense more or less fortuitous. 

 The fact that alkalin is a specific stain for resins might suggest a cor- 

 responding staining reaction in the case of rubber. As far as Sudan 

 III is concerned, however, we are employing a stain used in animal 

 histology to give definition to globules of fat occuri-ing in the cell. 

 Without going into the question of the chemisti-y and differential stain- 

 ing of the fats, fatty acids, and lipoids, it may be noted that the stain- 

 ing of fat globules by Sudan III is taken to indicate that this stain is 

 soluble in the contents of the fat globule whereas it is not solnblc in 

 the other constituents of the cell which, therefore, remain unstained. 

 It is somewhat difficult with this explanation of tlie characteristic 

 staining reaction of Sudan III in mind, to understand its action in 

 the case of rubber. This matter is mentioned simply to call attention 

 to the possible theoretical interest attached to the problem of the 

 staining of rubber inclusions in the cell. 



We have, further, been interested in this matter because cell in- 

 clusions have been consistently found in clilorophyllous tissue of both 

 stems and leaves which, with Sudan III, stained as rubber, but which 

 were difficult to differentiate witli this stain from tlie residue of the 

 protoplast witli its included chloroplasts, which does not in such tissiii' 

 entirelj' disappear after acetone extraction and which stains to some 

 extent with Sudan III. In this connection it should be stated that in 

 other tissues also it is difficult to distinguish between the protoplasmic 

 matrices of the c(^lls wliieh may be stained with Sudan III and the 

 rubber inclusions wliieh may oi' nuiy not be present. Thus in the 

 tables which follow it is in some cases possible that the plants which 

 on the basis of "microscopical examination" iwo stated to contain 

 "traces" of rubber may have shown only stained cell inclusions which 

 could not loositively be identified as rubber. 



We have made some preliminaiy investigation of the effects of a 

 variety of stains. A luimber of staining combinations were attempted, 



