V. 



SUB-CLASS II. 



rhodospermej:, or red algm. 



Diagnosis. Plants rosy-red or purple, rarely brown-red, or greenish-red. Fruc- 

 tljicatio7i o( two kinds, dioecious: — 1. fSpores {gemmidia, J. Ag.) contained either in 

 external or immersed conceptacles, or densely aggregated together and dispersed in 

 masses throughout the substance of the frond: 2. Tetraspores {splicer ospores, J. Ag. 

 gemmules, Thw.) red or purple, either external or immersed in the frond, rarely 

 contained in proper receptacles ; each tetraspore enveloped in a pellucid skin 

 (perispore) and at maturity separating into four sporules. Antheridia (not observed 

 in all) filled with yellow or hyaline corpuscles. Mar me, ivith one or two exceptions. 



The most obvious characteristic of the plants of this sub-class is their colour, thou"-h 

 this varies through every shade of red and purple into red brown, or pure brown ; 

 and degenerates, under the influences of sun-light and shallow water, into orange, 

 yellow, or dull green. Still, some faint tint of redness, or the absence of olive-green 

 or grass-green, prevents the student from confounding the faded Rhodosper niece with 

 either of the other groups into which the Algaj are divided. 



Their most remarkable and distinctive character however lies in their double 

 system of fructification ; two descriptions of spore-producing organs having been 

 found in almost all these plants, and always being developed on different individuals 

 of each species. Thus, these Algaj are strictly dioecious, though in a different 

 manner fi-om other dioecious plants ; for here it is not stamens and pistils (or their 

 analogues) which are borne on different roots ; but, some individuals of a species 

 produce only one kind of pistil or sporiferous organ, and others of the same species 

 constantly produce a sporiferous organ of a different kind. These diver.^e fructifi- 

 cations do not appear to be different phases of the same organ, like the two sorts of 

 flowers found in some Polygalce, Leguminosce and Malpighiacece, etc. ; but are in their 

 origin and development perfectly distinct, and formed with the greatest regularity, 

 following fixed laws. The spores developed in either system are equally capable of 

 reproducing the species ; and as the two kinds are always formed on different in- 

 dividual fronds, the idea of each species of these plants includes two individuals, 

 and is not complete unless both are known. Hence the necessity, in forming our 

 generic groui)s, to ground them on characters taken from the peculiarities of both 

 fructifications. 



Perhaps the natural explanation of this double fructification is to regard one form 

 of reproductive body as the true sp07-e, supposed to be fertilized tln-ough the agency 

 of an anthcridium ; and to consider the other to be merely a geuimule or bud, liere 



