REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 709 



wood, concerned in the transport of sap, through the trunks 

 of trees, can be proved, by electrical tests, to be fully 

 alive. This living wood responds to stimulation by in- 

 duced galvanometric negativity, such response disappearing 

 on the death of the tissue, as, say by drying, after which 

 it cannot be restored. The response of living wood is 

 also depressed by anaesthetics, and abolished by poisons 

 (figs. 216, 217). As regards the argument based on the 

 transport of poison, it has been shown that as the active 

 elements concerned in the transport of sap are diffused 

 throughout the length of the trunk, the death of one indi- 

 vidual zone, to which the poison has ascended, does not 

 abolish the suctional activity of the zone above. It is only 

 when the plant has been killed throughout, by the arrival 

 of the solution at its top, that the complete arrest of suction 

 could be expected to take place. And this is found to be 

 the case. Various agents, on the other hand, which are 

 known to induce changes, whether of exaltation or depres- 

 sion, in the physiological activity, are found to induce corre- 

 sponding modifications in the rate of suction. A very 

 delicate means of investigating this question has been 

 shown to be that afforded by the records obtained with 

 the Shoshungraph (fig. 218). Here, under the ordinary 

 method of record, the slope of the curve indicates the 

 normal rate of suction, and the effect of various agencies 

 is immediately shown by the resulting flexure of the curve. 

 This method of record, again, becomes extremely sensitive, 

 when it is carried out under balanced conditions. By means 

 of these records, it has been shown that depressing agents, 

 such as cold or anaesthetics, depress or arrest suction, 

 whereas warmth exalts it. It has been shown, further, that 

 just as the multiple activity of the Desmodium leaflet is 

 arrested, when the latent energy of the plant falls below 

 par, so also, under similar circumstances, the suctional activity 

 falls into abeyance, and that, as in the one case, so also in 

 the other, the activity is renewed, by the application of an 

 external stimulus. It has also been shown that the latent 



