164 Hydration and Growth. 



der of distilled water after being cut in halves. In a system of this kind 

 any alteration of the conditions which would facihtate 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 begin- 

 ning mid-forenoon at 20° to 22° C. and continuing until mid-afternoon, 

 when a fall in temperature brought transpiration to a rate below that of 

 accession from the stem. 



A large percentage of the nuts which were placed under the auxo- 

 graph lever were cast off at various stages of development by abscission 

 of the stalk. The inciting causes of the anatomical change which 

 results in 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 nights. Fin- 

 ally, an abrupt, rapid, and continuous shrinkage resulted in the separ- 

 ation of the stalk. 



The general features of growth of these nuts may be illustrated by a 

 r6sum6 of history of No. 10, which was under continuous observation 

 from July 15 to September 9, 1918, during which period of 56 days its 

 diameter increased from 16 mm. to 26.5 mm. Of this, 2.25 mm. was 

 gained in the first 5 days of cool, foggy weather. This effect was con- 

 firmed by the fact that a cessation or retardation occurred at midday 

 and was most pronounced on hot, sunny days, suggesting a direct 

 water-loss. In the week ending July 29 the total growth was an in- 

 crease of 1.7 mm. This period was characterized by heavy fogs and 

 mists in the forenoon, both the amount of shrinkage and rate of in- 

 crease being lessened — ^an equalization to be ascribed in part to ap- 

 proaching maturity. The temperature taken from a thermometer 

 thrust in a young branch of the thickness of the nut ranged from 13° 

 to 22° C. The completion of the record of No. 10 was followed by cut- 

 ting of the branch bearing it at a distance of 30 cm., placing the excised 

 end in water, and arranging the entire preparation in the dark room at 

 17° C, with the nut under the bearing lever of the auxograph. Swell- 

 ing continued for about 20 hours, after which shrinkage began, which 

 rapidly accelerated (see fig. 48). 



The general features of growth are also well illustrated by the 

 following notes on No. 15, which was brought under observation when 

 it was about 15 mm. in diameter and put under an auxograph ampli- 



