Macdougai^-hydration and growth. 



365 



and absorption. The nut in a growing condition has a high water 

 content, and a small unsatisfied capacity, but its supply from the 

 relatively dry stems must come slowly, so slowly that any marked 

 increase in transpiration would overbalance absorption in the nut 

 and result in cessation of enlargement or even shrinkage.^ 



Fig. I. Tracings of auxographic record of walnut (No. 15) during 

 three weeks. Variations are amplified forty-five times and the downward 

 movement of pen signifies enlargement. The scale is numbered in millime- 

 ters. Shrinkage during the midday period lessened by fogs and acceleration 

 in growth by the humidity and increased water supply from rain are among 

 the more striking features. 



Such retardation or apparent cancellation of growth by rapid or 

 excessive water-loss has already been discussed in connection with 

 the presentation of my original results dealing with the growth of 

 Opuntia. Recent exemplification of this action in Ccstrum noc- 

 tnrnum has been described by Brown and Trelease.* 



The fruit of the tomato (Lycopersicum) presents similar fea- 

 tures of behavior. The proportion of solid matter in young fruits 



3 MacDougal, D. T., " Reversible Changes of Form in Succulents." Re- 

 port Dept. Bot. Res. Carnegie Inst, of Wash. No. 14, p. 71. 1915. 



4 Brown and Trelease, "Alternate Shrinkage and Elongation of Growing 

 Stems of Cestrum nocturnuiii," Philip. Jour, of Science, 13 : No. 6. Bot. p. 

 353. November, 1918. 



