MacDOUGAL— HYDRATION AND GROWTH. 363 



A useful conception of the hydration conditions in the stems and 

 fruits may be formed, if due weight is given to the measurements 

 cited above. The woody branches of the previous year, on which 

 botn the leafy green twigs and those bearing the nuts are borne, had 

 a relatively large deficiency in water so that sections a few centi- 

 meters long absorbed about 20-25 per cent, of their volume of dis- 

 tilled water in 24 hours at 20° C. No swelling test was made, but 

 it is obvious that an enlargement of only a small fraction ought to 

 be shown by this or any branch with a mature woody cylinder. The 

 active green twigs still in a state of elongation arising from these 

 branches had a swelling capacity of 10 per cent. The growing nuts 

 arising from the drier stems exuded water from cut surfaces, the 

 cotyledons being sacs of watery fluid, in contrast to the dry ap- 

 pearance of sections of the youngest internodes, and showed a 

 swelling of less than 2 per cent, and soon shrunk when placed in a 

 cylinder of distilled water after being cut in halves. In a system 

 of this kind any alteration of the conditions which would facilitate 

 transpiration would have a differential effect on the older stems, the 

 green leafy twigs and the fruits. The loss from the stems would 

 be affected least since the bark would effectually prevent any notable 

 increase in evaporation from the relatively dry woody tissues. The 

 loss from the leafy twigs would of course tend to become greater 

 and the deficit in both leaves and twigs would be increased and their 

 absorbing power correspondingly increased. The outer integument 

 of the nuts being still in an embryonic condition and being highly 

 hydrated the loss would reach a maximum rate with the daily effect 

 of causing a cancellation of enlargement beginning mid-forenoon at 

 20-22° C. and continuing until mid-afternoon when a fall in tem- 

 perature brought transpiration to a rate below that of accession 

 from the stem. 



A large percentage of the nuts which were placed under the 

 auxograph lever were cut off at various stages of development by 

 abscission of the stalk. The inciting causes of the actual anatomical 

 change which cause the abscission lie outside the scope of this 

 article. It was noted however that it was preceded by a period in 

 which the nut showed a shrinkage by day in the higher temperatures 

 and lessened humidity, alternating with equalizing enlargements at 



