DEPARTMENT OF BOTANICAL RESEARCH. 65 



ities of such living material are not to be simulated by the imbibi- 

 tional action of the amino-compounds of gelatine, attention was paid 

 to the following matters : 



(a) Extractions from living cell-masses. 



(b) Extractions or solutions of sections of biocolloids. 



(c) Acidity of fresh or living tissues. 



(d) Acidity of desiccated tissues, 



(e) Swelling of fresh sections. 



(/) Re-swelling of extracted and dried tissues. 



(g) Swelling of dried tissues. 



(h) Repetition of swelling and drying treatments. 



These treatments as applied to median slices of maturing joints of 

 Opuntia discata grown at Carmel gave measurements as below at 18° C. 

 The flat joints at 10 to 12 mm. in thickness and the median portion 

 include but little chlorophyll. Sections suitable for swelling, free from 

 any except the smallest fibro- vascular strands, were readily procurable. 



The solution of material from a section of a plant with its thousands 

 of cellulose walls presents physical features that are not easily to be 

 duplicated. Amino-acids, hexoses, malates, and salts, however, con- 

 stitute the bulk of the extracted material, together with, other sub- 

 stances set free by the bursting walls of some of the cells, in addition 

 to those crushed in taking out the section. Diffusion of the pentosans 

 would take place slowly, although the derivation of large proportions of 

 this material by extraction after killing wath ether suggests that the 

 rate is not inconsiderable and may be subject to various modifications. 



The lessened hydration capacity of a section previously extracted 

 is probably a resultant of various losses. The amino-acids mixed with 

 the pentosans form a colloid with a high hydration coefficient. The 

 salts and free acids would operate to limit imbibition of a carbohydrate- 

 protein colloid and their extraction would remove this limit. Extrac- 

 tion may therefore remove acids and salts which lessen swelling, and 

 at the same time some amino-acids which give to pentosans a high 

 hydration capacity. The second swelling of a section of a plant may 

 therefore represent a series of reactions widely different from those of 

 the first treatment. 



We are indebted to Professor H. M. Richards for determinations of 

 the acidity of the "^vater in which fresh slices of Opuntia were swelled, 

 and it was found this might be expressed as follows: 10 c.c. solution 

 from dish in which set of fresh sections w^ere swelled in water = 0.44 

 c.c. N/20 KOH. Dried slices of the above material, when swelled in 

 water 24 hours, gave a solution the acidity of which might be expressed 

 as: 10 c.c. of solution = 0.10 c.c. N/20 NaOH. When such sections 

 were immersed in citric acid 0.01 N., the strength of the solution was 

 increased so that at the end of 24 hours the acidity was expressible as 

 10 c.c. of solution = 2.25 c.c. N/20 NaOH. 



