IN THE MOTOR ORGANS OP LEAVES. 



21 



of the cell-sap. This is demonstrated by the following experiments which were originally- 

 suggested by a paper, published in the year 1815 in the eleventh volume of the trans- 

 actions of the Linnean Society, and to which my attention was first directed br my 

 friend Dr. David Prain. It is entitled "On the Deoxidation of the Loaves of Cotyledon 

 calycina" (= Bryophyllum cahjeinum), and in it the author, Dr. lleyne, points out that a 

 i-onspicuous decrease in the acidity of the tissues (which he ascribes t<> processes of 

 deoxidation) takes place during the course of each diurnal period, alternating with a 



one.* 



corresponding increase in each nocturr 



On testing the leaves of Kalanchoe lacinmia it was at once ascertained that they 

 exhibited similar phenomena. Observations were first instituted during the course of the 

 hot season when transpiratory loss is very active diurnally, and when the amount of 

 fluid escaping on section of the leaves is much smaller in the evening than in the morn- 

 ing; but, in spite of this, it was at once evident that the acidity, and specially the fixed 

 acidity of the evening (and presumably concentrated) sap, was much lower than that of 

 the fluid escaping in the morning (plate III. fig. 2). Systematic i]m-tigati..n of the 

 subject afforded the following results: 



■ 



Experiment I. — Two leaves of Kalanchoe were taken, one, a, weighing IG'93 grammes, 



was 



and the other, b, 30*75 grammes. In both of them the reaction of the cell-sap 



highly acid at 10-30 a.m. when the experiment was begun. They were both exposed to 

 direct but broken sunshine beneath a tree, a being enclosed in a chloroform-chamber, 

 and b set with the base of the petiole in water. At 2 p.m. a weighed 12*2 grammes, was 

 of a pale ochreous olive colour and very flaccid ; whilst b was bright green and turgid, 

 and weighed 31'38 grammes. The sap of a was intensely and permanently acid, that 

 of b was even at first only faintly acid and only contained a mere trace of permanent 

 acidity. 





Experiment II.— A leaf of Kalanchoe, weighing 30*3 grammes, was exposed to direct 

 sunshine apart from water for three hours and a quarter. When first set at 10-30 a.m., 

 its juice was intensely acid. After exposure it weighed 28-48 grammes, and the 

 permanent acidity of the sap was very feeble. It was now set with the freshly divided 

 base of the petiole in water, and on the following morning the weight was 28*72 

 grammes, and the permanent acidity of the sap intense. 



Experiment III— A leaf of Kalanchoe, weighing 3058 grammes, and with highly acid 

 sap, was set with the base of the petiole in water in absolute darkness at 10-30 a.m. At 

 1-45 p.m. the weight had increased to 31 '08 grammes, and the acidity of the sap remained 

 apparently unaltered. 



* 



Experiment IV.— Two leaves of Kalanchoe, one, a, weighing 29*6 grammes, the other, 

 , 23*4 grammes, were set with the bases of the petioles immersed in water. The sap in 

 both of them was highly acid in reaction ; a was exposed to direct sunshine and b to 

 absolute darkness for more than three hours. At the close of this period a was slightly 

 limp, weighed only 27*7 grammes, and on section yielded comparatively little fluid, with 

 a mere trace of fixed acidity, whilst b was fully turgid, weighed 23*71 grammes, and 

 yielded an abundance of intensely and permanently acid fluid. 



* Transactions of the Linnean Society, vol. XI. p. 213. 



