202 SCIENCE PROGRESS 



in consequence of which the author is compelled to consider 

 Haberlandt's " pumping sieve-tube " theory. The conclusion 

 recorded in the paper previously referred to prompts the sug- 

 gestion that the seasonal changes in the nature and quantity 

 of the cell-sap solutes may be related to the need for retention 

 of water in drought or rest periods. In the same connection 

 may be noted the work of W. G. Craib {Notes jrom Bot. Card., 

 Edinburgh, 191 8, 11, 1-18) on the winter water storage in 

 deciduous trees. He found that during the period immediately 

 following leaf-fall the water in the trunk concentrates towards 

 the centre, beginning at the base of the tree. Later in the 

 winter, however, the reverse process takes place and the water 

 content of the peripheral layers increases at the expense of 

 the central portion, which eventually becomes the driest 

 region. In consideration, however, of the rather variable 

 relationship existing between heart-wood and sap-wood in 

 different trees, it appears unlikely that the course of water 

 movement here outlined can be a general phenomenon. It 

 would nevertheless be instructive to trace any changes in the 

 distribution of reserve substances in the trunk which might 

 accompany the translocation of water during the rest period. 

 W. H. Chandler {Univ. Missouri Agr. Exp. Station Research 

 Bull., 14, 1914, 491-552) obtained some noteworthy results in 

 his work concerning the competition for water by different 

 parts of the plant, and the part played therein by osmotic 

 phenomena, under arid conditions. He found that the osmotic 

 concentration of the sap of leaves and stem cortex was due 

 chiefly to non-electrolytes, except in the rather particular case 

 of succulents. The work of Lutman referred to earlier also 

 finds confirmation in Chandler's observation that there exists 

 a gradient of sap concentration in the cells of the cortex, 

 increasing from the roots to the topmost twigs. The question 

 of fruits is dealt with also in this paper, and it is noted that 

 the sap concentration in the leaves of common fruit-trees is 

 higher than that of the fruits themselves. This observation 

 explains the fact that fruits wither before the leaves during a 

 dry period, when the higher osmotic pressure of the leaf sap 

 constitutes a distinct advantage in the competition for water. 

 Moreover, it is shown that water will actually pass from fruits 

 to leaves under excessively arid conditions. In this connec- 

 tion the writer urges the necessity of adequate summer prun- 

 ing, which, whilst limiting root formation, nevertheless reduces 

 the risk of loss of fruit through withering. Ringing experi- 

 ments were also undertaken, and, in accordance with expecta- 

 tion, it was found that the removal of a ring of phloem resulted 

 in a lowering of the concentration of the sap in the region 

 below the ring, especially in the sap of the roots. 



