GoRHAM, Oil the Umbelliferie . 



17 



of distribution of the fibro-vascular tissue in leaves generally 

 are first considered. 



To prosecute the study of the venation in leaves with 

 advantage, it is necessary to have appropriate names for all 

 the varieties of veins that may possibly present themselves in 

 a perfectly formed leaf (netted), and then rigidly to classify 

 them, so that every leaf that may be presented for our inspec- 

 tion may have its proj)er place assigned to it as regards its 

 mode of venation. 



A perfectly formed netted leaf, such as we find in the lilac, 

 the rose, burdock, the peach, the nectarine, and in dicotyle- 

 donous plants generally, was chosen by Dr. Lindley for this 

 purpose ; and a reference to the mode in which any given 

 vein named in this leaf distributes itself in other leaves fur- 

 nishes at once a clue to their classification. 



The midrib (1, 1, Fig. I) in 

 a perfectly formed netted leaf, 

 sends forth alternately, right 

 and left, along its whole length, 

 ramifications. These are called 

 primary veins (2, 2, 2, 2). 

 They diverge from the midrib 

 at various angles, and pass 

 towards the margin of the leaf, 

 curving in their course, and 

 finally forming a junction or 

 anastomosis with the back of 

 the vein which lies next them. 

 That part of the primary vein 

 which lies between the junc- 

 tion thus described, having a 

 curved direction, may be called 

 the curved vein (3, 3, 3). Be- 

 tween this latter and the mar- 

 gin, other veins, proceeding 

 from the curved veins, occa- 

 sionally intervene. They may 

 be distinguished by the name of 

 external veins (4, 4, 4) . The 

 margin itself and these last are 

 connected by a fine network 

 of veins, marginal veinlets 

 (5, 5, 5).) Lastly, from the midrib are generally produced, at 

 right angles with it, and alternate with the primary veins, 

 smaller veins, which may be called costal veins (6, 6, 6). 

 The primary veins are themselves connected by fine veins, 



VOL. XVI. b 



Fig. I.— Netted leaf. 



1, 1. Midrib. 



2, 2. Primary veins. 



3, 3. Curved veins. 



4, 4. External veins. 



5, 5. Marginal veinlets. 



6, 6. Costal veins. 



7, 7. Proper veinlets. 



8, 8. Common veinlets. 



