ABSORPTION OF FOOD BY PLANT 363 



applied, and we observe the consequent depression of re- 

 sponse ; when the chloroform was blown off the responses 

 were found to undergo revival. 



In the next experiment, a specimen of living wood was 

 mounted in the vibrational apparatus, and its normal re- 

 sponses taken. I next applied copper sulphate, and the 

 record shows the consequent abolition of response (fig. 217). 

 I have thus been able to establish the fact that the woody 

 vessels of the sap-wood are not dead but living, and hence 

 fully susceptible of physiological reaction. This will, I think, 

 be found to dispose of one of 

 the difficulties raised in regard 

 to the physiological theory of 

 the ascent of sap. 



We come, secondly, to the 

 objections that have been based 

 on the ground of the ascent of 

 sap through a tree whose roots 

 have been killed by boiling 



FIG. 217. Photographic Record 



water, and, further, on the ex- showing Normal Responses ot 

 periments of Hartig and Stras- ^ a ^ , Tf 

 burger. These observers set cut Response by a Toxic Dose of 

 ends of trees in tubs of poisonous 



solutions, such as copper sulphate, which were found, in spite 

 of their toxic character, to ascend to the leaves. It is clear 

 that if such violent protoplasmic poisons ascend the trunk, 

 they must kill all the cells lying in their path. And from 

 this it was inferred that the living cells in the stem could 

 not be necessary to the rise of sap. Strasburger was thus 

 led to the conclusion that 'the supposition that the living 

 elements in any way co-operate in the ascent of the 

 transpiration current is absolutely precluded.' 1 



It does not, however, appear that this inference on the 

 part of Strasburger was justified, for we must remember the 

 fact that any cut piece of stem when placed in s water is found 

 to exhibit suctional activity. Hence the active cells con- 

 cerned if the process is to be regarded as due to such 



1 Strasburger, Text-book of Botany (English translation), 1903, p. 188. 



