68 TRANSLOCATION IN PLANTS 



every other leaf, for example, will alter the sugar water, and 

 nitrogen content of the remaining leaves. 



In the summer of 1930 I carried out a rather extensive 

 series of tests to determine if there were diurnal variations 

 in the water, nitrogen, and dry-matter contents of leaves 

 of Ailanthus. Eighteen matched pairs of vigorous shoots 

 of Ailanthus were selected for the experiments. On each 

 shoot six leaves were tagged and numbered in order. 

 No. 1 being a young leaf near the terminal bud which 

 was still growing. This younger leaf had not reached its 

 maximum size nor had leaf 2. Number 4 had probably 

 completely ceased growing. Leaf 6, though the oldest 

 leaf used in the experiment, was not the oldest on the 

 shoot, but was still well colored and apparently functional. 

 Still older leaves were in some cases becoming yellow, and 

 in a few instances abscised during the experiment. Shoots 

 1 and 2, 3 and 4, 5 and 6, etc., were matched one with 

 the other. In some cases they were forks on the same 

 saplings, in others two separate stems, although these 

 probably arose as sprouts from the same root system. 

 Each leaf bore from 15 to 20 pairs of well-matched leaflets. 

 One half of the leaflets were taken at the beginning, and 

 the second half at the end of each 12-hour period. Col- 

 lections were made night and morning; those for the day 

 period were harvested at 7 a.m. and 7 p.m., while those 

 for the night period were harvested at 7:30 p.m. and 7:30 

 A.M. One hundred and forty-four samples were taken in 

 all, so that there were 72 sets, 36 showing the change in 

 composition during the 12-hour period during the day, 

 and 36 for the 12-hr. night period. After analyzing 72 

 samples it became evident that, though there were distinct 

 diurnal variations in absolute dry-matter content of the 

 leaflets, there were no consistent changes in either total 

 water or total nitrogen content, except in the younger 

 leaflets which were not mature. It is to be noted that 

 these younger leaflets which were still growing showed a 

 gain in fresh weight and nitrogen content both during 

 the day and during the night. There is an indication 



