MORPHOLOGY OF THE VEGETATIVE ORGANS 107 
have broad, comparatively short blades. In some cases the broad 
blades are unsymmetrical, one side being much wider than the 
other. These oblique blades are common in Olyree. 
In contrast to the broad surface mentioned above, the 
blades may be very narrow, when they are said to be 
filiform or capillary. Often the blades are rolled, thus 
appearing much narrower than they are when unrolled. 
Convolute blades are those in which one margin is rolled over 
the other. Involute blades are those in which both margins are 
rolled inward toward the center, the upper surface being inside. 
Revolute blades are those in which the margins are rolled outward, 
the lower surface being inside. Conduplicate blades are folded so 
that the upper surface of the two halves come in contact as in Poa 
Fendleriana and its allies. In common blue-grass one may observe 
all gradations between flat and completely conduplicate blades. 
Certain blades that appear to be rolled may be thickened into a 
slender terete or cylindrical form, the upper surface being repre- 
sented by a mere groove (forms of Festuca ovina, Andropogon 
Urbanianus). 
Petiole—In some leaves especially those of shade 
grasses mentioned above, there is a more or less well- 
marked petiole at the base of the blade. 
Examples: Orthoclada, Senites, Ichnanthus, many bamboos. 
137. Nervation.—The vascular system of the grass 
blade consists of a strong main central axis, the midrib, 
and few to several smaller bundles called nerves, on each 
side parallel to the midrib. These nerves are continua- 
tions of corresponding nerves in the sheaths and they can 
usually be traced with the naked eye through the region 
of the collar. The anastomosing bundles, or cross-veins, 
are usually indistinguishable to the unaided eye. The 
broad blades of shade grasses (except Pharus and Lep- 
