UPWARD TRANSPORT OF NITROGEN 61 



were taken at daily intervals up to a week. Though the 

 data do not show differences that are statistically sig- 

 nificant, and therefore are not presented, they indicate a 

 gradual day-to-day increase in nitrogen of the leaves of 

 the check plants above that in the ringed. They show no 

 hint of excess in the ringed over that in the check at any 

 period during the experiment. 



The data of Maskell and Mason indicate a diurnal 

 variation in nitrogen and ash contents of leaves. If the 

 diurnal variation is real, it is conceivable that the ring, by 

 preventing the removal from the leaves, makes it appear 

 as if these leaves had actually imported more than the 

 check leaves, whereas it is possible that they had merely 

 exported less, either because the ring had prevented 

 export, or because the higher carbohydrate content had 

 enabled the leaves to retain more nitrogen as well as other 

 mineral elements. In interpreting the data of Maskell and 

 Mason (1929a) it should also be remembered that only 

 three days before the experiment started the basal part 

 of each stem was cleared of all leaves and branches for a 

 distance of two feet. This would tend to result in a 

 distinct decrease in the carbohydrate content of the plant 

 as a whole and thus would favor a more rapid transport 

 of carbohydrate and nitrogen from the remaining leaves 

 of the check plant. The ring would prevent such trans- 

 port from the leaves of the ringed plant. Saposchnikoff 

 (1890) observed that the leaves of Helianthus plants, from 

 which all but two leaves were removed, lost dry weight 

 at the rate of 0.653 g. per square meter per hour, while 

 leaves of plants with fourteen leaves lost at the rate of 

 only 0.198 g. per hour. The plant with leaves reduced to 

 one-seventh the number lost 3.3 times as fast. With 

 Cucurbita, a plant with two leaves remaining lost dry 

 weight at the rate of 0.449 g. per square meter per hour, 

 while a plant with six leaves lost at the rate of 0.269 g. 

 per hour. No mention is made as to the proportion of 

 leaf surface removed in the work of Maskell and Mason, but 

 the effect would tend to accentuate removal from the 



