94 



Hydration and Growth. 



41.9 



the hydroxid, and least in the organic acids mentioned, in propor- 

 tions of 40, 20, and 15 in Rudheckia, and 30, 25, and 15 in Micrampelis. 

 Phytolacca gave proportions of 30, 25, and 12 under the same circum- 

 stances. It was noticeable that distension due to swelling by these 

 acids was relaxed after a few hours, probably due to the solution out 

 of some of the colloidal contents of the cells. 



Further tests were made with the stalks of Rudheckia bearing heads 

 of flowers about ready to open. The greater part of the total growth 

 had been accomplished, although they were still in rapid action and 

 the material for the developing flowers was being drawn from them. 

 Tangential slices less than 1 mm. in thickness were removed, leav- 

 ing the stalks 4 mm. in thickness at 

 the larger end and about 3.4 mm. at 

 the smaller. Sections about 1 cm. in 

 length were cut from four such stalks 

 and the whole number was divided into 

 two lots. One lot of sections was taken 

 into the dark room and swelled at 

 18° C. and the others were set on a 

 window-ledge to become air-dry. The 

 average thickness was taken to be 3.7 

 mm. Twenty hours later swellings of 

 6.8 per cent in distilled water, 4.8 per 

 cent in alkali, and 1.4 per cent in acid 

 had been made (fig. 17). Actual en- 

 largement by imbibition in the acid had 

 lasted only about an hour, after which 

 a shrinkage ensued that reduced the 

 thickness 5.4 per cent from the original 

 volume and 6.8 per cent from the max- 

 imum. The decrease here and the in- 

 crease in water and in hydroxid were 

 all in progress at the close of the test. 

 The dried sections came down to about 



half of their original diameter, but, on account of the irregular 

 shapes assumed, could not be measured with accuracy. Trios of these 

 under the auxograph gave swelhngs of 41.9 per cent in distilled water, 

 21.6 per cent in hundredth-normal citric acid, and 37.8 per cent in 

 hundredth-normal sodium hydroxid. The sections were thus seen 

 to return to about their original size in the living condition in dis- 

 tilled water — nearly this size in hydroxid, but far short of it in 

 the acid solution, after the manner of a salted biocolloid consisting 

 of a large proportion of carbohydrate and a smaller one of protein. 

 Here, as in all comparisons between the hydration of living and of 

 dried sections, it must be taken into account that in the desiccation 



Dried 



Fresh 



6.8 



37.8 



sections 



material 

 4.8 



21.6 



Water Alkali Acid 



Fig. 17. — Swelling reactions of fresh 

 and dried flower-stalks of Rud- 

 heckia, in percentages of original 

 thickness. The proportionate in- 

 crease of dried sections is denoted 

 by the heights of the vertical lines, 

 and that of fresh sections by the 

 marks near base. 



