60 



THE CAUSES OF FLUCTUATIONS IN TUMESCENCE 



pair of pinnae are in close contact with one another and with the lateral surfaces of 

 the rachis. Up to this time the midrib remains somewhat elevated at an acute angle to 

 the 



of the rachis, but subsequently dep 



gradually sets in, so that tl 



poster! 



and anterior edges of the lam 



come in the first 



t 



lie 



ipectively 



horizontally superior and inferior, and ultimately to be directed downwards and forward 

 at angles of varying degree of obliquity from the line of the rachis. (Plate II, Fig. 2.) 



The motor organs which det 



this 



developed and pi 



certain 



plicated series of 



mov 



pecu 



their action. 



Both 



which greatly facilitate a comprel 



highly 

 ion of 



composed of two distinct mas>es of 



perficially and in section it is at once evident that they are 



of which is of 



warm ochreous and the 



other of a vivid green colour, and that these hold certain definite positions in relation to 



the deeply keeled 

 of the base of 



bundle of the pulvin 



and 



the under and upper surfaces 



the outer side of the 



outer half of the lamina. 'J he ochreous tissue lies beneath 

 vascular bundle and spreads out thence over the under surf 



,nd to 



ice of 

 the base of the outer half of the lamina so as to involve and conceal the origins of 



the lowest four 



five rib 



The 



gx 



perior to the vascular bundle and forms an 



face of the 



half of the lamina 



, on tin 

 expansi 



other hand, lies internally and 



over the base of the 



The disp 



pper 



f the two masses of tissue 



is clearly shown in Figure 19 of Plate I and Figure 3 of Plate II, and the laminar 



expansion of the ochreous tissue in Figures 4 and 5 of Plate II 



distinct masses of pulvinar 



We have 



to deal 



one 



superior, the other extero-infer: 



m relation to the pulvinar vascular bundle and the base of the outer half of the lamina, 

 and differing greatly in the amount of their chlorophyll content. Now, it is clear that 



any alteratio 

 flexible axis 



ith varying deg 



the relative strengths of masses of 



disposed around a central, 



must tend to give rise to movements of divergence or convergence, combined 



of dep 



and of 



ding a* the aW««, implies increased strength in one or the other mass (Plate 



Fig. 6). Were they merely related to the axial bundle 



other direction 



VII 



to diver 



»..» 



or convergence, dep 



they would give 



rise 



only 



similar to those which we find manifesting themselves 



bipinnate leaves; but the movements 



because they represent the outcome of 



distributed between the secondary petioles and The 



or elevation, and we should have movement 



are in this case farthe 



which in the case of 



the secondary petioles of many 



iplicated by rotation, 



bip 



leaves are 



bundle is determined by the relations which the 

 to the inferior and superior surfaces of the r 



pinnules. The rotation of tl 



al 



pposed masses of pulvinar tissue hold 



infero-extemal mass is expanded 



gidly 



panded lamina 





of the lamina, whilst the green intero-superior 



over the base of the inferior surface of 



upper surface of the 



must tend 



depress, the 



irea, and 

 and any 



nsequentl 



hold 

 any 



s a 



The ochreous 

 the outer half 



to th 



half of the lamina, and theref 



strength in the latter 



ard rotation or torsion of the flexible 



to 

 bundl 



(ponding relation 

 strength in the former 

 mass must tend to 



cause corresponding inward or 



expanded, we should have had movements of elevation and 



JV 



foldi 



dep 



np of the outer half of the lamina 



of the midrib and 



mating with movements of 



movements do 



h 



tually occur at a particul 



expansion of the lamina ; and 



amina not rigidly 

 f the midribs and 



divergence and 

 as a matter of fact such 



the lamina becomes 



period in the life of the pinna. Wr 



previously g 



rise to movements of 



,'idly and permanently expanded 



folding and 



th 



factors which 



unfolding do not 



cease to exist, but 









