Chap. XIII.] RE-EXPANSION. 269 



The Re-expansion of the Leaves. This is effected at an 

 insensibly slow rate, whether or not any object is enclosed.'* 

 One lobe can re-expand by itself, as occurred with the 

 torpid leaf of which one lobe alone had closed. We have also 

 seen in the experiments with cheese and albumen that the 

 two ends of the same lobe can re-expand to a certain extent 

 independently of each other. But in all ordinary cases both 

 lobes open at the same time. The re-expansion is not de- 

 termined by the sensitive filaments; all three filaments on 

 one lobe are cut off close to their bases ; and the three leaves 

 thus treated re-expanded, one to a partial extent in 24 hrs., 

 a second to the same extent in 48 hrs., and the third, 

 which had been previously injured, not until the sixth day. 

 These leaves after their re-expansion closed quickly when 

 the filaments on the other lobe were irritated. These were 

 then cut off one of the leaves, so that none were left. This 

 mutilated leaf, notwithstanding the loss of all its filaments, 

 re-expanded in two days in the usual manner. When the 

 filaments have been excited by immersion in a solution of 

 sugar, the lobes do not expand so soon as when the filaments 

 have been merely touched; and this, I presume, is due to 



snonding process In the excitable during the first tenth. If we as- 



tlssues of animals. sume that the distance travelled 



Certain unpublished re- by the disturbance Is one ceutl- 



searches made during the last meter, this gives 100 miUimctera 



two years have led Professor prr second as the rate of propaga- 



Sanderson to extend his views In tion. This, as Professor Sander- 



the direction above Indicated, son has pointed out, happens to 



and to conclude that the " leaf- be just about the rate of propaga- 



current," *. e. the electrical dif- tlon of the excitatory electrical 



ference between the upper and disturbance In the muscular tls- 



lower surfaces of the leaf, Is In- sue of the heart of the frog. 



tlraately connected with the P. D.] 



physiological conditions of that " Nuttall, In his ' Gen. Amerl- 

 part of the upper surface from can Plants,' p. 277 (note), says 

 which spring the sensitive flla- that, whilst collecting this plant 

 ments: thus It will probably be In Its native home, "1 had oc- 

 establlshed that the " leaf-cur- caslon to observe that a detached 

 rent " and the excitatory disturb- leaf would make repeated efforts 

 ance are dlflTerent manifestations towards disclosing Itself to the 

 of the same property. F'rom Influence of the sun; these at- 

 nieasurements made with his tempts consisted In an undula- 

 Rheotome, of six carefully chosen tory motion of the marginal clllse, 

 leaves, taken from vigorous accompanied by a partial open- 

 plants (Aug. 188"), Professor Ing and succeeding collapse of 

 Sanderson found that the elec- the lamina, which at length ter- 

 trlcal disturbance produced In minnted In a complete expansion 

 one lobe by stimulation of the and In the destruction of sensi- 

 other by an Induction current, be- blllty." I am Indebted to Pro- 

 gins In the course of the itecond fessor Oliver for this reference; 

 tenth of a tecond following the but I do not understaud what 

 excitation. . In five out of the six took place, 

 leaves no effect was perceptible 

 18 



