132 



D. T. MacDOUGAL AND H. A. SPOEHR 



in the salt. It is notable, however, that only in the acid solu- 

 tion did an extraction take place in consequence of which the 

 sections when dried and rehydrated failed notably to come back 

 to an approximation of the original. 



Other preparations were made in which the sections included 

 a portion of the clear parenchyma as well as of the chlorophyl- 

 lose layer and the epidermis. These were first hydrated, then 

 desiccated and swelled a second time at 16 to 18°C. The increases 

 were as below: 



First swelling. . . 

 Second swelling. 



WATER 

 DISTILLED 



CITRIC ACID 

 O.OlN 



100 



225% 

 107 



SODIUM 



HYDRATE 



O.OlM 



281% 

 87.5 



POTASSIUM 



NITRATE 



O.OlM 



287.5% 

 137.5 



The first swelling of the dried material agreed with the 

 measurements of the series described above in showing the 

 greatest expansion in the salt, and a greater relative hydration 

 capacity in the alkali than in the first series. The striking 

 feature of this pair of tests however is the notable reduction in 

 hydration capacity of material which had been previously 

 treated. Such reduction obviously can not be ascribed to coagu- 

 lation, but must be attributed to the effect of extractions, other- 

 wise it would have been shown in the first swelling after drying. 

 This extraction had the greatest effect in the alkali and was 

 not widely different in water, acids and salts. The difference 

 between the behavior of these sections and of the previous pair 

 may be safely attributed to the presence of some diffusible 

 substance affecting imbibition present in the chlorophyllose 

 layer. 



That this hypothetical material or combination is however 

 not characteristic of chlorophyll-bearing tissues is shown by the 

 behavior of another Opuntia. 



A spineless Opuntia from Mexico which had been obtained 

 from Mr. David Griffiths of the United States Department of 

 Agriculture several years previously showed less mucilage than 

 O. discata and other forms from Tucson. Dried median slices 



