IRRITO-COXTRACTILITY IX I'LAXTS. 199 



primary petiole is 48-55 m. m. If a bit of ice or a drop or two 

 of ice-water be applied to its distal end, the petiole will fall in 

 as short a time as already stated. This shows that in the 

 primary petiole at least, the rate of propagation is not less than 

 25 m. m. per second, a rate quite equal to that met with in the 

 contractile tissues of various animals. 



Confirmatory evidence is got by the use of various chemicals. 

 When a minute drop of carbonate of ammonia is delicately 

 placed on the tip of a young leaflet, one notices \.\\?Ci for the first 

 4-4^ seconds a change in color or density gradually creeps doivn 

 the leaf substance, but b}' the time that this has spread over half 

 the leailet contraction ensues, and thereafter the other leaflets 

 close at the time rate already given for them. But even by the 

 time that the second or third pair has contracted, twitching and 

 partial closure of pairs near the leaf base prove that the stimu- 

 lus has already travelled down the secondary mid-rib greatly 

 faster than is indicated by the movement of the leaflets. 



Ether is a very serviceable stimulant, though I will not now 

 enter into disputed questions as to the action of its vapor. A 

 small drop of 20/0 ether was placed on one of two end 

 leaflets. The others closed in succession within 8 seconds, the 

 leaf fell at 14 seconds, within 18 seconds the leaf next above 

 fell, and within 3 1 seconds the leaf still higher. From the 

 leaflet tip to the pulvinus of the last mentioned leaf, the distance 

 was 160 m. m., so that the average rate of propagation necessary 

 for movement of parts was, at least, 5 m. m. a second. Guided 

 by Elfving's experiments on various of the lower plants, where 

 he found that 2 to 5 /o chloroform and 1 5 '/o ether might not 

 prove permanently injurious to some organisms, experiments 

 were made with 6 fo ether. When a drop was applied to the 

 tip of a leaflet very slight movement followed in most instances; 

 in three cases there was a half-closing of the terminal leaflets, 

 and in one only did they close, to re-open again in 4I- minutes. 

 In two of them the second and third pairs of leaflets were 

 visibly affected and slightly moved upward and forward. No 

 injurious effect followed the application. 



Hot water and heated wire applied to any part of the petiole 

 or of the leaflets stimulate rapidly. 



