392 



Intramarginal Vein, and other notes on Venation. 



The following preliminary remarks apply, to venation in general : — 



" The distribution of the strands (technically known as veins, ribs and nerves) traversing the green 

 tissue is connected in the closest manner with the structure and shape of the leaf-blade. The term vein 

 has some justification, since most of these strands contain cells and vessels which serve to conduct fluid 

 materials to and fro ; but since there are also strands which have nothing to do with this conduction, which 

 are developed exclusively for the support of the whole blade, the name is unsuitable, and can only be used 

 figuratively." (Kerner and Oliver " The Natural History of Plants," I, 628). 



" If soaked in water, the epidermis and thin- walled green tissues decay, while the tougher strands 

 remain intact. We term these skeletons, though not quite correctly. 



" The fact should be emphasised that the distribution and arrangement of the strands in any given 

 species is remarkably constant. This, however, is by no means the case in genera and families. Of 

 course, there are plant families, the whole of whose members exhibit marked agreement in this respect, as, 

 for example, the . . . Myrtaceae." (p. 635.) 



There is, however, much variation in the venation of leaves of individual 

 species of Eucalyptus. This has been shown abundantly at p. 394, &c., and in the 

 illustrations and text of the present work. Mr. Henry Deane (below) refers to the 

 subject. 



Coming to the intramarginal vein, the position of this vein is stated in its name, 

 and it is most evident in the juvenile stage, where it is often at a considerable distance 

 from the margin in the youngest leaves, receding towards the margin as growth 

 proceeds. But it does not appear to be a definite entity in the same way that the 

 secondary veins are that emerge from the midrib, but an anastomosis of the ends of 

 such veins. Bentham's definition of (or reference to) the vein will be referred 

 to presently. 



The intramarginal vein was earliest referred to by A. P. de Candolle, in 

 Prodromus, iii (1828), and in G. Don's translation of the same in 1832 (already referred 

 to at p. 357). 



Bentham (B.F1., iii, 185) has the following passage : — • 



". . . . the primary veins often scarcely perceptible when the leaves are thick; in some species 

 few, irregular, oblique, and anastomising and passing through every gradation from that to numerous 

 parallel diverging or transverse veins, always converging into an intramarginal vein, either close to or 

 more or less distant from the edge . . ." 



In the same work he employs the intramarginal vein to some extent in specific 

 descriptions. 



Mueller in " Eucalyptographia " adopts intramarginal vein, and introduces a 

 new equivalent, " circumferential vein," sometimes " irregularly remote from the 

 edge of the leaf." The word " circumferential " was the word Mueller preferred in 

 later years, for he did not share Huxley's dictum (see Part L, p. 312) as to the 

 undesirability of coining new terms and definitions when equivalents were already 

 *n use. 



