Imbibition and Growth in Fruits. 171 



sustained a changing relation as growth slackened. The enlargement 

 of such highly watery fruits must be so largely a matter of diffusion 

 and hydration that any formula expressive of the temperature re- 

 lations of chemical transformation must be wide of the facts in many 

 stages of development. 



The record of growth of No. 3, which is given in full in figure 50, 

 shows beyond question the effect of transpiration and water-loss on 

 growth. As the daily temperatures of the fruits rose from 12 C. and 

 14 C. to 26 C. and 28 C., acceleration ensued up to a point where 

 the rise caused a water-loss overbalancing the gain by hydration. 

 Higher temperatures, therefore, did not facilitate or accelerate growth 

 unless accompanied by high relative humidity. Thus the highest 

 growth rates are those of midday and afternoon, with fog or showers. 

 This is especially marked on the records of September 10, 11, 12, and 

 13, in which a 50-hour rainy period was anticipated and followed by 

 high humidity. (See fig. 50.) It was not possible to increase the 

 water-supply by watering the soil around the roots in such manner as 

 to cancel the midday shrinkage or slackening in growth. One espe- 

 cially striking effect is that in which the rise in temperature conse- 

 quent upon the cessation of the rain, from 20 to 25 C. at 3 p. m. on 

 September 13, was followed by a lessened rate of growth. On the 

 cloudy days growth was uniformly high. Similar effects were exhib- 

 ited by a small fruit of a potato in a greenhouse at Tucson in May 

 1918. 



The two types of fruits are seen to show a concordant behavior with 

 respect to the balance between the water-supply and transpiration. 

 A rise in temperature with accompanying lessened relative humidity 

 had the effect of retarding or stopping growth or of producing an actual 

 shrinkage in volume. The nut and the berry are both more highly 

 hydrated or more watery than the stem through which their water- 

 supply must be drawn. This was established by measurement in the 

 walnut and is obvious with respect to the tomato and its stems. 



A distinction must be made between the water-relations of a fruit 

 and its stem and that which prevails between a parasite and its host, 

 or between a swelling colloid and the solution in which it may be im- 

 mersed. The water deficit of the stems as measured by swelling in- 

 cludes that of the entire structure. The fruits, however, receive their 

 supply through special conduits which sustain only a mechanical rela- 

 tion to the other parts of the stem which may be active in its swelling. 

 Such non-cctaducting tissues of course draw their supply from this 

 system of conduits also, but it is highly probable that the dispropor- 

 tion between the water-content of the fruit and of the tracts in the 

 stem from which it receives its supply is not so great as might be 

 indicated by the measurements given. The hydration capacity of the 

 fruits would be the resultant of many factors, including the pentosan- 



