ON THE IRRITABILITY OF VEGETABLES. ^5 



ready to retract ray opinion, unci with the greatest pleasure 

 give to her the merit of having explained that which has 

 puzzled many physiologists. 



On the Irritability of the Vessels of Plants. 



As almost every vegetable physiologist has treated of Ascent of the 



the ascent of the sap, and as the irritability of the V es- s:ip , < ' >niu ' c ' wi 



. . ." w: t'' the irri- 



sels is intimately connected with this operation, this sub- tability of the 



ject becomes extremely interesting. Van Marum, in a vessels ' 



paper addressed to Jngenhousz which is contained in 



the Journal cte Physic) ue for September 179-2, notices 



some experiments, which had been made by Coulon, 



and then proceeds to mention some electrical experiments, 



which he himself had made on plants. He first makes a This irri'abi- 



few observations on the destruction of the irritability of the li! >> like that 



muscular fibres, and then reasons thus: If the contraction s t roved bv' 



of the vessels of plants is the effect of their irritability, it electricity. 



will be destroyed in the same manner as the irritability of 



the muscular fibres, lie adds: *' I tried if this would hap- 



*' pen in the summer of last year upon some species of eu- 



" phorbia, which have the common property of giving out 



44 much milky sap from their wounds. I caused the stream 



" of the grand Teylerian machine to pass through the 



" branches of euphorbia latbyrus, and through the twigs of 



" euphorbia campestris, and eyparissias, and I observed, 



" that all the branches or twigs of these plants, which 



" conducted the stream or the electrical torrent during 



" twenty or thirty seconds, absolutely when they were cut 



" did not give out any more sap from their wounds. 



" 1 repeated these experiments with the branches of the 



" fig-tree, which a!*o gave out milk by their wounds. The 



" effect was perfectly the same; the sap was not seen to flow 



" out when the branches were cut, after they had eouduefc- 



'• ed the electrical torrent during five seconds ; but when 



'? the electrified branches were pressed between the fingers, 



" a little sap could be perceived to flow, which rendered it 



" evident, that the electrical torrent had not emptied the 



" electrified vessels, by forcing the sap low aids the- roots 



fa » but 



