Grinnellia americana, Harv.. 3 



of GHnnellia, 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. 



B a 



