504 



SCIENCE 



[N. S. Vol. XLIV. No. 1136 



previous paragraph. The results compared 

 with the swelling of gelatine were as follows: 



As the plant did not show water relations 

 which might be interpreted as a mechanical 

 resultant of the separate action of gelatine or 

 agar it was next proposed to test the reactions 

 of a mixture in which these substances would 

 be blended, which was done in July, 1916. The 

 first test mass was one consisting of about 

 equal parts of agar and gelatine, though the 

 quantities were not weighed. Both were 

 soaked and melted separately and the gelatine 

 was poured into the hot agar which was kept 

 at a temperature of about 90° C. for a half 

 hour. The mass was then poured on to a glass 

 slab for cooling. Two days later it was 

 stripped off as a fairly clear and transparent 

 sheet slightly clouded, the average thickness 

 of which was 0.2 mm. Strips about 5X7 mm. 

 were placed under the apices of sheet glass tri- 

 angles in glass dishes after the manner in 

 which plant sections had been tested, and 

 auxographs were arranged to record the ac- 

 tion of acids, alkalies and distilled water. 

 The first trial made on July 21 gave the fol- 

 lowing final relative size of the strips as com- 

 pared with the original: distilled water 850 

 per cent.; nitric acid (hundredth normal), 725 

 per cent.; hydrochloric acid (hundredth nor- 

 mal), 750 per cent.; sodium hydrate (hun- 

 dredth normal), 950 per cent. No record of 

 the temperature of the room was kept. A sec- 

 ond test on the following day at temperatures 

 of 61°-65° F. gave the following: distilled 

 water, 675 per cent.; hydrochloric acid, 625 

 per cent.; nitric acid, 687.5 per cent.; sodium 

 hydrate, 750 per cent. These results were 

 taken to be of such importance that a series 

 of mixtures of agar with 20, 50 and 80, 95 and 

 99 per cent, of gelatine by dry weight were 

 made up. The mixtures were poured into 

 moulds on glass plates and dried sheets from 

 0.1 mm. to 0.6 mm . in thickness were obtained. 



The measurements given below include the re- 

 sults of tests under varied conditions not only 

 of thickness of the samples, but also of tem- 

 perature, length of period of swelling, tension 

 of instruments, etc. Each set of three meas- 

 urements of the swelling in the three liquids 

 is therefore to be considered separately, and is 

 not to be compared with one above or below, 

 either as to amplitude or relative swelling, as 

 the experiments were varied in many ways. 

 For the sake of completeness some results with 

 agar and with gelatine alone are included. 



The outstanding fact that a mixture con- 

 sisting mostly of gelatine, to which a small 

 proportion of agar has been added, shows its 

 greatest swelling in alkaline solutions is the 

 most important feature of these results. The 

 mixture in question is available as a physical 

 analogue which has already been found useful 

 in the study of growth and swelling of plants. 



