IN THK MOIOX ORGANS OF LKA\ IS. 



it 





In the case of another leaf, of which careful weight. aents were nude, tho result 



were as follow 





1. "Weight of entire leaf 



• • ft 



• ■ • 



,K i7 grammes. 



2. Weight of primary petiole, including primary pulvinus ... 007 



3. Weight of primary pulvinug ... 



• • • • •• 



oi „ 



4. Weight of secondary pulvini, secondary petioles nnd pinnules ... tH<) „ 

 "). Weight of primary petiole without the primary pulvinus ... 06 „ 



The 



he noted are, int tl 



le 



to which tin- pr 



mary pulvinus is exposed (vide Appendix A), and, * W, tho excessive transpiratorv 



"lities Which are provided by llio I minar surfaces. Takinfr the data derived fi«.m th 



fae 



second leaf in which the weight of the primary pnlvinus was determined, it 



pj>eais 



that the pnlvinus had to support a weight forty -six times as gr« at as its own, and of 

 which 80 per cent, was situated at the distal extremity of an elongated rigid lew . 



penor epi 



represented by the primary petiole. The pow- r in this lever lystem U) applied at tho 



immediate neighbourhood of tho fulcrum, and the Weight is MtMrteil at tho end of a 



long lever— conditions implying extreme instability of equilibrium in event of am 



fluctuations in the power. The excess of trmispiratory facilities furnished by the 



laminar surfaces is mainly due to the fact that both tho inferior and si 



are provided with »tomata (Plate V, Figs. H, 10). The numbers of stomal a on th« 



inferior epidermis are not in excess, but rather fall short, of those pr >ent on the 



inferior surface of tho pinnules of PUkecMimm unman-, but in tho latter, as well 



as in tho other nyctitropic leaves which have been specially considered here, the 



superior epidermis is entirely wanting in tin m. Additional facilities for the occurrence 



of active transpiratotw loss are, moreover, provided by the extremely open chai cter of tho 



yma intervening between the pallisade cells and tho ini nor epidermis (Plate \ 



Fig. 11). There are thus structural grounds for assuming that a ry active trans- 

 piratory loss of fluid must occur under favourable circumstances and that such !«»,- 



ally takes place is demonstrated by the following experimental data 



Experiment I. — A pot-plant of Mimosa jnulJca bearing seven leaves was taken. The 

 hole in the bottom of the pot wee firmly corked, and the entire outer surface and lip 

 were thickly coated with melted wax. A glass plate, largo enough to cover the mouth 

 was then divided into two halves, and a small piece was filed out in tho centre line of 

 division, so that when tho halves were adjusted to one another they formed a plate with 

 B small central perforation. These were next luted down with melted wax over the 

 mouth of the pot, so that the lower part of the axi* of tho plant passed through tho 

 • entral opening and, finally, the line of division and the opening were also carefully- 

 luted. The pot was next placed in an hermetically-closed chamber containing a vessel 



the weight of which had been determined, and which contained 50 grammes of pure 



iuric acid, and the whole apparatus was set in the open air in diffused sunlight. 

 The leaves remained in a state of extreme expansion and elevati »n. At the close of four 

 hours the sulphuric acid was removed and weighed, and tho weight amounted to 51*0 

 grammes, indicating an absorption of 1*6 grammes of water of transpiration. The acid 

 was now returned to the chamber, and the latter anew hermetically sealed, and on the 

 following day it weighed 54- 1 grammes, corresponding to an absorption of 4-\c.c. of 



during the period of twenty-four hours. The cover of tho pot was now 



remov 





