MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 341 



Water. HClN/ioo. NaOH N/ioo. 



Gelatine 25 — Agar 75. 



378.0 427-3 510.7 

 Gelatine 20 — Agar 80. 



1 144-5 572-1 526.0 



Gelatine 10 — Agar go. 

 looo.o 401.0 300.0 



Gelatine I — Agar gg. 

 1825.0 475-0 4250 



The data indicate that as the proportion of agar in the mixture 

 is increased, the relative ampHtude of swelHng in water may be 

 increased, and the relative amount of imbibition in acid is decreased. 

 This superior imbibition capacity in water as compared to efifects 

 of acid and alkali is a fair parallel to the behavior of sections of 

 young, mature and old parts of Opuntia. 



The second parallel of importance is the one in which the 

 swelling in alkaline solutions is in some cases less and in others 

 greater than in acidified solutions in mixtures containing as much as 

 a third or more of agar. 



The mucilaginous material which may be obtained by macerating 

 joints of cacti in distilled water is fairly similar to agar. Some of 

 this was used in mixtures in place of agar. The averages of a series 

 of swellings of a mixture of 90 parts of gelatine and 10 parts of 

 such mucilage, reckoned by dry weight, were as follows : 



Water. HCI X loo. NaOH N/ico. 



428.1 per cent. 770.4 per cent. 557-8 per cent. 



These data are of interest when compared with the swellings of 

 mixtures of 100 parts gelatine to 5 parts agar, and of mixtures of 

 80 parts of gelatine to 20 parts of agar (see p. 340). The mucilage 

 from joints of Opuntia affects the swelling of gelatine in much the 

 same manner as does agar in equivalent proportions. The watery 

 extract of course contains the soluble salines of the plant, and some 

 of the effect might be attributed to their presence. 



A few simple tests were arranged to show the effects of a salt 

 on the colloids used, the results of which are as follows : 



