70 CARNEGIE INSTITUTION OF WASHINGTON. 



tion could of course take place only by the absorptive or imbibitionary 

 action of colloids rather than osmosis. 



The fruit of the tomato {Ly coper sicum) presents some daily varia- 

 tions similar to the walnut and is characterized by a dry weight which 

 lessens proportionately with development. Four fruits less than a 

 week old, with radial diameters of 14, 16, 17, and 18 mm., were found 

 to weigh 14.650 grams. These were fragmented and dehydrated, 

 showing a dry weight of 1.90 grams. From this it is to be seen that the 

 young fruit contained 87 per cent of water and 13 per cent of dry 

 material. Mature fruit of the same kind weighed 93.050 grams and 

 contained 8.400 grams dried material, being 9 per cent of the total. 

 These watery fruits showed in a very marked manner the effect of 

 water-loss or transpiration on the growth of the fruits. As the daily 

 temperatures of the fruits rose from 12° and 14° C. to 26° and 28° C, 

 acceleration ensued up to a point where the rise caused a water-loss 

 overbalancing the gain by hydration. Higher temperatures, there- 

 fore, did not facilitate or accelerate growth unless accompanied by 

 high relative humidity. Thus, the highest rates are those of midday 

 and afternoon, with fog and showers. This is especially marked in a 

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

 high humidity. 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 at other times. 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. was 

 followed by a lessened rate of growth, and the rate on the cloudy days 

 was uniformly high. 



The water deficit of the stems as measured by swelling includes that 

 of the entire structure. The fruits, however, receive their supply 

 through special conduits which sustain only a mechanical relation to 

 the other parts of the stem, which may be active in its swelling. Such 

 non-conducting tissues of course draw their supply from this system 

 of conduits also, but it is highly probable that the disproportion 

 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-protein 

 ratio, the hydrogen-ion concentration, the action of salts, and the 

 effect of the amino-compounds, and the course of growth does not 

 follow the above daily procedure in all plants. I have described in 

 previous publications the manner in which the concurrent action of 

 transpiration, nydration capacity of the cell-colloids, and temperature 

 cause the highest rate of growth in Opuntia in the daytime. This 

 behavior is conditioned on the fact that the cacti show the greatest 

 transpiration at night, at which time the acidity rises until it is ten 

 times as great as in the daytime. 



