Chap. XVI. MOVEMENTS OF THE LEAVES. 875 



tain whether a fluid would act as energetically as a substance 

 yielding the same soluble matter to the glands. No distinct 

 difference was perceptible; certainly none in the degree of in- 

 curvation ; but the incurvation round the bits of sponge lasted 

 rather longer, as might perhaps have been expected from the 

 sponge remaining damp and supplying nitrogenous matter for a 

 longer time. The margins, with the drops, became plainly 

 incurved in 2 hrs. 17 m. The incurvation subsequently increased 

 somewhat, but after 24 hrs. had greatly decreased. 



Experiment 13.— Drops of the same strong infusion of raw 

 meat were placed along the midrib of a young and rather deeply 

 concave leaf. The distance across the broadest part of the leaf, 

 between the naturally incurved edges, was '55 of an inch (13-97 

 mm.). In 3 hrs. 27 m. this distance was a trace less ; in 6 hrs. 

 27 m. it was exactly '45 of an inch (11'43 mm.), and had therefore 

 decreased by '1 of an inch (2*54 mm.). After only 10 hrs. 37 m. 

 the margin began to re- expand, for the distance from edge to 

 edge was now a trace wider, and after 24 hrs. 20 m. was as 

 great, within a hair's breadth, as when the drops were first 

 l^laced on the leaf. From this experiment we learn that the 

 motor impulse can be transmitted to a distance of "22 of an 

 inch (5*590 mm.) in a transverse direction from the midrib to 

 both margins; but it would be safer to say '2 of an inch 

 (5*08 mm.), as the drops spread a little beyond the midrib. 

 The incurvation thus caused lasted for an unusually short time. 



Experiment 14. — Three drops of a solution of one part of 

 carbonate of ammonia to 218 of water (2 grs. to 1 oz.) were 

 placed on the margin of a leaf. These excited so much secretion 

 that in I h. 22 m. all three drops ran together ; but although the 

 leaf was observed for 24 hrs., there was no trace of inflection. 

 We know that a rather strong solution of this salt, though it 

 does not injure the leaves of Drosera, paralyses their power of 

 movement, and I have no doubt, from the following case, that 

 this holds good with Pinguicula. 



Expei'iment 15. — A row of drops of a solution of one part ot 

 carbonate of ammonia to 875 of water (1 gr. to 2 oz.) was placed 

 on the margin of a leaf. In 1 hr. there was apparently some 

 slight incurvation, and this was well marked in 3 hrs. 30 m. 

 After 24 hrs. the margin was almost completely re-expanded. 



Experiment 16. — A row of large drops of a solution of one 

 part of phosphate of ammonia to 4375 of water (1 gr. to 10 oz.) 

 was placed along the margin of a leaf. No effect was produced, 

 and after 8 hrs. fresh drops were added along the same margin 

 without the least effect. We know that a solution of this 



ir 



