10 FRANCIS E. LLOYD 



visually appreciable flaccidity, the fluctuation in question is 

 apart from the loss from wilting in the usual sense and may be 

 considered chiefly as a fluctuation above and below a normal, 

 or perhaps better, average quantity. That however this fluctua- 

 tion is, for the far greater part, within the leaf, and not the stem 

 would be expected from the fact that the potometer was used, 

 and this is shown by a determination of the amounts of water in 

 the leaves of the ocotillo at various times of the day and night. 



The method employed was the following. Leaves were col- 

 lected into a tared bottle, and the fresh and dry weights deter- 

 mined. The amount of water was calculated to the dry weight 

 of the leaves. The results obtained from six series, thr.ee on each 

 of two different occasions, on August 11 and August 16 are given 

 in tables VI and VII respectively, from which it is seen that the 

 percentage of water to dry weight varies from about 225 to 300 

 per cent as extreme limits as between day and night. The two 

 curves in the figure are for the average of the members of the two 

 series taken separately. They show that the diminution in the 

 amount of water in the leaf begins at daybreak and continues 

 until sometime between noon and 4 p.m. The behavior of the 

 leaf in this regard is in general harmony with that indicated by the 

 transpiration curve during the earlier half of the day, namely, 

 that the outgo of water exceeds the income. The period of recov- 

 ery, however, as indicated by leaf-water determinations is not as 

 evidently indicated by the transpiration data, save, probably 

 by piece 3, in which there was a substantial net gain. In pieces 

 1 and 2 there was a net loss. This partial discrepancy may be 

 explained on the theory that the net loss in the afternoon is felt 

 by the stem-tissues rather than those of the leaves, these experi- 

 encing a net gain. However, it must be remembered that the 

 leaf samples were obtained from other plants, in situ, on other 

 days than that in which the transpiration observations were made. 

 Should there have been some interference to the entrance of water 

 into the cut surface of the stem in the potometer pieces (and this, 

 in spite of the precaution taken, is not unlikely), it is quite possible 

 that a state of negative pressure might have made itself evident 

 in the stem, while the increasingly less favorable conditions for 



