ON THE IRRITABILITY OF VEGETABLES. QJJ 



ed in vessels, and if we can prove, that these vessels are irri- be irritable, we 



table, then we can very easily transmit the analogy to the t n , 18y in er » that 

 ' . the sap vessels 



Sap vessels. The experiments of Van Marum go far to are also. 



establish the irritability of the vessels, which contain that 



secreted fluid ; but the following, which I have made more 



than once, appear to me conclusive on the subject. 



Having a number of plants of the euphorbia helioscopia, Experiments 

 Icutoffthetop of one, and found, that the milky juice flowed. ollthe sub J ect " 

 copioufly. I now submitted this plant to the electric influence 

 for some seconds by passing sparks* through it, which were 

 so small as seldom to be visible. I then cut the stem about 

 the middle, and but very little juice flowed. I next covered, 

 the end of the remaining half with a little moss, and placed 

 the root in water. For some days it seemed languid, but in 

 a few more began to recover. Soon after this I cut the 

 stem across about two inches from the root, and the milky 

 juice flowed abundantly. 



In this experiment then we find, 1st, that the milky juice 

 was expelled by the contraction of the vessels. 2dly, That 

 the electrical fluid weakened the irritability of the vessels, 

 but did not destroy it, or kill the remaining half of the 

 plant: and 3dly, That after a certain time, when the plant 

 had recovered from the shock, the milky sap was again ex- 

 pelled by the contraction of the vessels. This experiment 

 also shows, that Sennebier's suspicion concerning the disor- 

 ganization of the parts of the euphorbia helioscopia is 

 groundless. 



I have repeated some of Van Marum's experiments with Van Marum's 

 the same results as himself. The last mentioned experi- [j^jjjj 5 ' 

 ment, is rather a delicate one, for it is difficult to regulate 

 the electric stream so as that it will only hurt the irritabi- 

 lity of the vessels without killing the plant; but should it 

 prove successful in the hands of others, I should then be 

 disposed to think, that the irritability of th"e vessels, which 

 contain this secreted milky fluid, will be established on a 

 sure foundation never to be overturned. 



* Or rather the stream. 



IV, 



