Some Hydration Reactions and Growth. 



159 



of the temperature of the ah", which in this setting must have been 

 practically identical with that of the inclosed pod (fig. 45). The air 

 inside this chamber was at a high degree of humidity, and it was 

 found that the afternoon cessation or retardation of growth was not 

 so marked in actively growing pods and that it did not come on so 

 early in the development of the pod as in those exposed to the 

 evaporating influence of the freely circulating air. The influence of 

 high humidity approaching saturation was shown more directly by the 

 application of wet slips of filter-paper in such manner that the pod 

 was completely swathed and evaporation reduced to a minimum. 

 This treatment was also successfully applied to pods resting upon a 

 cork base and not inclosed in the chamber. When a slowly growing 

 young pod was thus given an atmosphere of high humidity at tem- 

 peratures from 20° to 27° C. no alteration in the rate would be visible 

 for nearly an hour, but at the end of this time an abrupt acceleration 

 would ensue which would continue for as much as 2 hours, and then, 

 if the supply of moisture were not renewed, a slackening would ensue 

 which would bring the rate back to the point at which it was growing 

 previous to the treatment (see figs. 46 and 47). 



Fig. 46. — Tracing of auxographic record of pod of Phaseolua which was 2 mm. in thickness at 

 beginning of record. Downward movement of pen denotes increase in thickness, X 45. 

 The range of active growth lies between 15° and 30° C. and consequently acceleration ensued 

 in the morning, retardation occurred as temperatures about 30° C. were reached in the after- 

 noon, and the rate increased again at sunset, when the temperature fell to a point below 30° 

 C, but slowing down followed in the cooler night temperatures. 



Fig. 47. — Tracing of auxographic record of variations in thickness of young pod of bean. The 

 enlargements caused by humidity are seen a.t 1, 2, and 3. 



The greater part of the enlargement registered in the above measure- 

 ments was due to the growth of the beans, and the imbibition capacity 

 of such seeds has been measured separately. A. Dachnowski (see 

 reference, p. 63) found that mature seeds absorbed and held more 

 water in acids and hydroxids than in distilled water at temperatures 

 not given, and that the amounts taken up in alkaline solutions was 

 greater than that in acids. The general imbibition reactions, in my 

 own experiments, of young seeds which had reached a thickness of 



