332 



character of the spores, for here we arrive at a clear resem- 

 blance to the metamorphosis of flowering plants. In flowering 

 plants ihe Jioiver is a truncated branch, and all its parts are 

 metamorphoses of leaves ; this flower produces seeds. In the 

 algse of which we speak, the ceramidium (or spore case) is a 

 truncated branch, and its parts are modifications of the apical 

 fibres or supposed leaves ; this spore-case produces spores. 

 Seeds in the first case, and spores in the second, are thus 

 formed, so far as we can perceive, under analogous circum- 

 stances. It is therefore not unreasonable to infer that the 

 bodies so formed are analogous to each other. The same can- 

 not be said respecting tetraspores. One step in the analogy 

 is, however, deficient. We know in what manner the germs 

 of seeds are fertilized, but we have yet to learn under what 

 circumstances this alteration in the condition of spores takes 

 place, whether previous to the growth of the ceramidhim, 

 when the spore may be supposed to exist under the form of a 

 naked ovule, or subsequent to the formation of the ceramidium, 

 and full organization of the spore. I am not prepared with 

 any evidence on this most obscure subject. 



" I shall only further remark, as strengthening the analogy 

 derived from the metamorphosis of flowering plants, that in 

 Polysiphonia the antheridia (or supposed stamens) are formed, 

 as the spores appear to be, by a metamorphosis of the cells of 

 the apical fibres. In flowering plants we know that stamens 

 and pistils are merely modifications of a common type, altered 

 for a special purpose. And here we find that spore and anthe- 

 ridium have a common origin, each in the apical fibre; but 

 spores are produced when the branch is metamorphosed into a 

 conceptacle, and antheridia are formed on the fibres of the 

 unchanged branches, and developed externally." 



Dr. AUraan, in confirmation of Dr. Harvey's views, referred 

 to the fructification the Charce, whose whorls arc regarded by 



