212 



The Ottawa ISIaturalist. [March 



attraction due to transpiration at the leaf above, and also by 

 '• root-pressure" from below. Mr. Shutt stated that root-pressure 

 was not well understood, that it could not be accounted tor on 

 physical grounds alone, and that we must assume that the vital 

 activity of the cell plays an important part in the rise of the sap. 

 The flow of sap in the maple was then discussed in detail. For 

 many of the facts upon which he based his statements, Mr. Shutt 

 said he was indebted to Bulletin 103 of che Vermont Agricultural 

 Experiment Station, copies of which, to a limited extent, the Direc- 

 tor of that Station had kindly placed at his disposal for distribution 

 among the members of the Club. At the Vermont Station it was 

 established that pressure and flow went hand in hand. Pressure 

 is a cause of the flow, but not the sole cause. Cold nights fol- 

 lowed by warm days make the ideal sugar weather. Uniform 

 temperatures, whether high or low, do not favor a flow of sap. 

 The higher temperature, following cold nights, seems to excite the 

 protoplasm to activity. The root-hairs absorb water, and since 

 there is no transpiration, as the buds have not opened, the water 

 accumulates in the tree, setting up a high pressure. Pressure is 

 further increased by the expansion of the gases in the tree due to 

 the rise in temperature. Tapping the tree relieves this pressure. 

 The water, in escaping, carries out with it in solution the sugar 

 which was stored from the previous season in the tissues of the 

 sap-wood. The direction of the movement is principally through 

 the Xylem vessels and downward through the phloem elements, 

 but it is also in every direction, more or less, depending upon 

 pressures, and these again chiefly on changing temperatures. In 

 summer the movement is generally upwards. 



The lecturer closed his interesting address by pointing out 

 the utility of a knowledge of plant physiology. To instance but 

 one of several illustrations, he gave his studies and experiments 

 on apple twigs, which show-ed him that the greater the water- 

 content of the twigs the less hardy they were. This being true, 

 it is obviously advantageous to reduce, if possible, the amount of 

 water in the tree, at the close of the summer, to enable it to with- 

 stand the severe conditions of a winter season. Cultivation of 

 the soil of an orchard should not, therefore, be continued in the 

 autumn. A "cover" crop, sown in July, withdrew the moisture 



I 



