12 THE CAUSES OF FLUCTUATIONS IN TUKGESCENCE 



Experiment II. — A leaf of Kalanchoe, weighing 11 6 grammes, was immersed for half 

 a minute in water at a temperature of 90° C, and then, after being gently dried, set in 

 a hermetically closed chamber. Visible exudation began to appear on the surface within 

 five minutes, and within four hours it had assumed a yellowish olive colour and weighed 

 only 10*1 grammes. On the following morning it had lost 0*4 grammes more, giving a 

 total loss of l'9c.c. of fluid, or 16 per cent, of total weight. 



Just as in the case of leaves treated by exposure to chloroform, the amount of loss 

 of fluid taking place from the tissues varies according to the time of year, presumably 

 in relation to the age of the leaf and the area presented by the intercellular spaces, or 

 to the precise nature of the osmotic products present in the cell-sap at different seasons. 

 For example, whilst in the two previous experiments, which were conducted in January, 

 when the leaves are in a dormant condition as regards growth, the losses in weight 

 amounted respectively to 19*3 and 16*3 per cent, of the total, whilst in one carried out 

 in the end of May the total loss amounted to only 40 1 per cent. 



Experiment III. — A leaf of Cassia sumatrana with eleven pairs of pinnae was taken, 

 and the centrally situated pair and the corresponding portion of the rachis were dipped 

 into boiling water. The boiled pinnae became - flaccid at once and dropped vertically 

 downwards from the petiole, with their upper surface looking directly outwards. The 

 base of the petiole was now freshly divided under water, and the leaf, along with a check 

 one, set to stand in a bottle of water in the open laboratory. The boiled pinnae had at 

 once assumed a yellowish olive tint and presently became distinctly yellow, the colour 

 being quite distinct from that following prolonged exposure to chloroform. A certain 

 amount of tendency towards the assumption of the normal nocturnal position manifested 

 itself in the pair of pinnae immediately beyond the boiled portion of the petiole 2 but 

 this had completely disappeared within the course of three hours. On the following day 

 the boiled portions of the leaf were yellowish-brown and dry, whilst the proximal and 

 distal portions were green and turgid. The pinnae of the distal portion were, however, 

 more or less in the nocturnal position, this being, no doubt, due to the fact that, whilst 

 the conduction of water through the wood remained unimpaired, the dead superficial 

 tissues of* the boiled portions of the leaf presented a site of abnormally excessive 

 evaporative loss, as indicated by their dry condition. 



Experiment IV. — A leaf of Cassia sumatrana, like the preceding one was taken and 

 the fourth and fifth pairs of pinnae with the corresponding portion of the rachis were 

 dipped into boiling water. Immediate and total depression of these pinnse occurred and 



was 



followed by a partial assumption of the nocturnal position in the sixth pair 

 The base of the petiole was now freshly divided under water and luted into a water-bottle 

 in a hermetically sealed chamber. The sixth pair of pinnae rapidly resumed the fully 

 expanded condition, and yellowing of the fifth and sixth pairs and of the corresponding 

 portion of the rachis soon manifested themselves, the surface of the rachis at the 



same 



time becoming studded by an exudation of drops of fluid. On the following day the 

 boiled pinnae were quite flaccid, moist and yellowish -brown, and the corresponding 

 portion of the rachis was covered by large drops of brownish fluid, while all the rest 

 of the leaf was turgid, bright green and fully expanded. It was now removed from the 

 chamber and set in the open laboratory, and, in a short time, the drops of exudation 

 disappeared from the boiled portion of the rachis and simultaneously the distal intact 



