104 PROCESS OF NUTRITION. CHAP. III. 



summer, is by no means so favourable to vegetation 

 as the milder though more changeable temperature 

 of spring and autumn, yet it does not wholly 

 suspend the movement of the sap. Palms may be 

 made to bleed at any season of the year. And al- 

 though this is not the case with plants in general, 

 yet there is proof sufficient that the colds of winter 

 do not, even in this climate, entirely prevent the 

 sap from flowing. Buds exhibit a gradual develop- 

 ment of parts throughout the whole of the winter, 

 as may be seen by dissecting them at different 

 periods. So also do roots. Evergreens retain their 

 leaves ; and many of them, such as the Arbutus, 

 Laurustinus, and the beautiful tribe of the Mosses, 

 protrude also their blossoms, even in spite of the 

 rigour of the season. But all this could not pos- 

 sibly be accomplished if the motion of the sap were 

 wholly suspended. 



Itsdirec- The sap then is in perpetual motion with a more 

 o'f ascent, accelerated or more diminished velocity throughout 

 the whole of the year: but still there is no decided 

 indication, exhibited in the mere circumstance of 

 the plant's bleeding, of the direction in which the 

 sap is moving at the time ; for the result might be 

 the same whether it was passing from the root to the 

 branches, or from the branches to the root. But as 

 the great influx of the sap is effected by means of 

 the pores of the epidermis of the root, it follows 

 that its motion must, at least in the first place, be 

 that of ascent ; and such is its direction at the sea- 



