124 U2^ITED STATES GEOLOGICxYL SURVEY— TERTIARY FLOEA. 



Considering the secondary veins in relation to tlieir mode of expansion 

 into the leaves, they are named : — 



1. CraspeAodrome, when they reach and penetrate the borders in passing 

 up from the middle nerve. The leaves with a nervation of this kind arc more 

 generally dentate or lobed. These nerves are either simply craspedvdrome, 

 when they join the borders without branching, as in the Chestnut, the Beecli, 

 etc., or doubly craspedodrome, when they branch and join the borders with all 

 their divisions or some of them only, as in the Birch, the Hazel, the Elm, etc. 



2. Caiyiptodrome, when the primary areas which they limit do not reach 

 to the borders. Then the nerves curve inside of the borders, and thus they 

 inclose the outside borders of these areas. The secondary nerves either curve 

 quite near the borders, and the veinlets which go out of the flexure imme- 

 diately enter the margin, or the primary areas do not extend so far, the 

 secondary veins curving and becoming united nearer to the midrib, and thus 

 a series of secondary areas is formed between the borders and the bend of the 

 secondary nerves by successive divisions ; these are named marginal areas, 

 and, when in many rows, may be distinguished as inner, middle, and outside 

 areas. They may be named also, in considering especially the nerves, festoons, 

 or hows, single or multiple, with the same appellation for their range, except 

 for the border area, which is generally called marginal. When, by anasto- 

 moses, the veins form a series of meshes, which, distinct, decrease in size from 

 the lower part of the areas to the borders, this nervation is named brachio- 

 dronie. 



3. Marginal nerves are those which, going out from the midrib at the 

 base of the leaves, follow close to the borders and parallel to them. They are 

 not secondary nerves, for these, passing up along and from the midrib, join 

 the marginal veins along the borders; they form a true border line, which 

 generally curves inside at the point of union to the secondary veins. This 

 nervation characterizes a large number of leaves, especially of the Myrtacece, 

 the Proteacece, the MtjricacecE, etc. A fine representation of it is seen in 

 Myrica Torreyi (pi. xvi, figs. 4, 8, and 9, of this volume). 



4. Mixed nerves are seen upon leaves where the secondary nerves are on 

 one part craspedodrome, while on the other they are camptodrome. This is 

 often seen in lobatc leaves, where some of the secondary nerves ascend to 

 the point of the lobes, while, above it or under it, others curve along the 

 borders, as in the leaves of the Tulip tree, for example. 



