Grinnellia americana , Harv. 
3 
of Grinnellia , it should be said that in well-developed plants 
lateral veins arise from the basal region of the percurrent 
midrib. In frayed fronds these lateral veins occasionally 
develop into strong branches, simulating the action sometimes 
occurring at the tip of the frond after an injury to the apex ; 
viz. bifurcation of the midrib in its subsequent growth. Often 
these proliferations are the only vestiges of the frayed frond ; 
and thus is demonstrated the fact that clusters of young 
plants can arise vegetatively by compounding the remnants 
of the old one. In this respect Grinnellia resembles closely 
the associated genus Delesseria. 
The leaf-like frond is supported by a short somewhat 
cylindrical stalk which terminates in a dense, disk-shaped 
holdfast. As Mr. M. C. Potter suggests in his study of the 
thallus of Delesseria , this differentiation of parts in the frond 
of Grinnellia gives the single plant a resemblance in structure 
and functions to a dicotyledonous leaf. The foliar expansion 
serves as an organ of assimilation ; the midrib, veins, and 
stalk furnish channels for conducting food-material and 
reservoirs for its storage. This last function is evidenced 
by the initial growth of numerous proliferations from the 
midrib and stalk of frayed fronds. 
Both asexual and sexual reproduction prevail in Grinnellia 
americana ; and, unlike many of the Florideae, monoecism is 
never present. The two methods of reproduction and the 
differentiation of the sexes give certain peculiar character- 
istics to the vegetative structure of the different fronds. 
Male plants are usually much smaller, less abundant, and 
have more delicate fronds, than either female or asexual 
individuals. The largest dimensions of those collected at 
Woods Hole were 7 cm. wide and 15 cm. long. The fronds 
have a smooth surface, and, if superficially examined, would 
be considered sterile ; but a careful inspection reveals numerous 
lighter-coloured portions occupying from two to many times 
the area of the normal cells. Sections through these areas 
show them to be patches of antheridia producing large 
numbers of antherozoids. 
