CLASSIFICATION. 3 



Melanospermeae), all the olive-coloured ; and Ceramiaceae 

 (our Rhodospermeae), all those of a red colour. I think no 

 student of marine plants, who is acquainted with the meaning 

 attached to the words " natural order " among flowering 

 plants, will consent to apply this term to either of the three 

 groups here indicated. 



It is not that each of these groups is not a natural assem- 

 blage, but that it is a group of much higher value than an 

 order, and must be regarded as a Series or Alliance, consist- 

 ing of several orders. The orders of which each group con- 

 sists, while they agree in some general features, differ one 

 from another both in the composition of the frond and of the 

 fructification. Thus Fucus and Ectocarpus have a certain 

 relation to each other, but it is distant; and in the structure 

 of their frond and fruit there is that dissimilarity which for- 

 bids these genera being associated within one order. So also 

 of Polysiphonia and Delesseria, or other widely dissimilar 

 genera of the series of red Algae ; or of Codium and Nostoc 

 among the green kinds. These genera therefore we regard 

 as examples of separate orders in parallel series. 



The series are, however, not strictly parallel. If we closely 

 examine the organization of each it will be found that the 

 Chlorospermece or green Algae are the simplest in structure ; 

 that their lowest members are the least compound of all vege- 

 tables, some consisting of a single cell, others of a string of cells 

 linked together, end to end ; and that the most developed of 

 this group are not on a par with the least complex of either 

 of the other groups. The inferiority of the green Alga? is 

 therefore generally admitted. But it is less clear to which of 

 the others, the Rhodospermeee and Melanospermea, the palm 

 of superiority ought to be given. Formerly the Melanosper- 

 meae were regarded as the most perfect. The great size 

 attained by several of this group, the perfect foliage and dis- 

 tinct organs of fructification of others, seemed to give them 

 eminence : while the delicacy and intricacy of structure of 

 many of the Rhodospermeae, and above all, the more full 

 development of their spores,* which are uniformly parted at 

 maturity into four sporules, entitle this group, in the opinion 

 of several modern writers, to the highest place in the class. 

 Many of the olive group have, however, an equal complexity 

 of spore, and others (as Sargassum) show a clearer distinc- 

 tion in the frond into leaves and stem and fructification than 



* Sphaerospores, Ag. ; tetraspores, Dne. ; granules, Grev. ; gemmules of 

 others. 



B 2 



