1902 I NOTES ON SASSAFRAS 431 



the blade, A pair of secondaries or tertiaries branches from 

 the petiole at the juncture of the leaf-blade and forms its 

 ascending margins, becoming slightly separated where the latter 

 curves outward — a short distance above the base of the primary 

 the lowest lateral curves toward the margin ; just before reaching 

 the margin it forks, the lower short branch joining the marginal 

 vein and the other branch curving upward ; the former together 

 with the marginals form a rough inverted isosceles triangle, whose 

 base is usually approximately on a level with the point of inser- 

 tion of the primaries or slightly higher. This arrangement 

 occurs in all the normal leaves examined by me, numbering sev- 

 eral hundred, and in the abnormal forms it occurs in all but seven 

 specimens out of 229. I fail to find this feature in any of the 

 published figures of fossil forms, but it is a character which would 

 be easily obliterated or overlooked, as marginal veins would not 

 be distinguishable from margins unless they were of considerable 

 size or the matrix were exceedingly fine-grained. A remarkable 

 character of the modern lobed leaf, first pointed out by Lester 

 F. Ward^, are the marginal veins at the bottom of the sinuses. 

 In the normal trilobed leaf about half the distance from the 

 lateral primaries to the tip of the leaf is traversed before the first 

 pair of secondaries branch from the midrib ; the interval is filled 

 with cross and horizontal veins which belong to the tertiary sys- 

 tem ; the secondaries in question leave the midrib at usually a 

 wide angle, and curving upward pass directly to the sinuses. 

 Here they are not lost but fork at a wide angle, often 160°, the 

 two branches following the margins of the sinus for more or less 

 distance until they leave them to' join the branches given off 

 from the primaries below and the next pair of secondaries above. 

 This is nearly a constant feature of the modern leaf, recurring in 

 substantially the same manner in all forms of the leaf, whether 

 2, 3» 4, 5, or 6-lobed. In leaves in which the sinuses approach 

 the midrib closely there are numerous tertiary veins passing 

 directly from the midrib to the sinus and from the primary to 

 the sinus, joining its marginal vein. Just w^hat purpose is served 

 by this marginal vein in the economy of the leaf is difficult to 



■^Buli. 37, U. S. Geol. Survey, p. 61. 



