ABSORPTION OF FOOD BY PLANT 355 



induced by these. The results obtained, at least with the 

 specimens which I have tried, are in general parallel to those 

 obtained by the electrical form of stimulation. Thus, in 

 young roots, in the majority of cases, when subjected to the 

 action of so dilute a solution as -5 per cent, of sodium car- 

 bonate, an electrical change of galvanometric negativity was 

 induced. The continued action of this solution, however, 

 tended to induce a reversal to galvanometric positivity. But 

 the reactions of older roots were different that is to say, in 

 the greater number of the latter cases, a solution of *5 per 

 cent, induced galvanometric positivity ; and it required a 

 much stronger solution, of from 5 to 10 per cent, to bring 

 about the reaction of galvanometric negativity. 



We have thus seen that in the root, as in the digestive 

 organ, there are alternating phases of secretion and absorp- 

 tion, and that it is by means of the secreted fluid that solid 

 inorganic substances are rendered soluble, for subsequent 

 absorption as food. We have seen moreover that the elec- 

 trical reactions in the two cases are similar ; that in the 

 young root, as in the young glandular organ of Nepenthe, the 

 characteristic response is by galvanometric negativity ; and 

 that long-continued stimulation induces diphasic variation, 

 with a tendency towards the reversal to positive. We saw 

 further that older roots, like the glands in the older pitchers 

 of Nepenthe^ have a phasic reaction which is predominantly 

 positive. And now, having thus completed our first line of 

 inquiry, we shall turn to the second the question, namely, 

 as to whether the ascent of sap is or is not essentially due to 

 physiological reaction. 



The possible explanations of the ascent of sap may be 

 grouped broadly under two different heads, as either physical 

 or physiological. Under the former of these must be named 

 such theories as those of atmospheric pressure, capillarity, 

 osmosis, and evaporation from leaves. Under the latter, 

 the physiological, the movement of water is regarded as 

 mainly due, in some hitherto undefined way, to excitatory 

 actions by which the sap is propelled in a uni-directioned 



