4 RHODOSPERME.E. v. 



of infernal structure which prevails among plants tliat have externally a close resem- 

 blance. This last peculiarity compels us, in order to understand their true affini- 

 ties, to acquire an intimate knowledge of the anatomy of the frond ; and this is only 

 to be learned, in the compound species, by a patient examination of transverse and 

 lono-itudinal slices, always a tedious, and sometimes a difficult process. In the 

 o-eneric distribution proposed by the earlier systematic writers, the external form 

 of the conceptacle, or the colour and substance of the frond, were chiefly considered ; 

 in most cases, irrespective of the anatomic structure. Thus, plants the most oppo- 

 site in internal composition, and producing fructification fundamentally diverse, were 

 often placed in the same genera. A notable instance of such unnatural association 

 occurs in the old genus, Spha;rococcus^ Ag. which included almost every round- 

 fruited species which had no other " local habitation or name ;"* and this at the 

 arbitrary will of the author, for the generic character assigned to the assemblage 

 could not be said to apply to a tithe of the species placed in it. Dr. Greville first 

 reformed this group, separating Wiochjmenia, Gracilaria, Chondrn.i, Phyllophora, 

 Gelidium., Gigartina, Hypnea, and Iriclcm from it, a sufficient evidence of the chaos 

 it then contained. No doubt Dr. Greville's system was a vast improvement on that 

 of the elder Agardh ; but his genera were often founded on the external habit of 

 the frond, and sometimes included plants as little related naturally to each other 

 as those placed in the old group SpJuerococcus. Thus, Rhodymenia, Grev. comprised 

 all the old SpJuiTOCOCci with a red, expanded, membranous, ribless frond, no matter 

 what the internal structure of the frond, or of the fructification. Examination has 

 shown the structure of both frond and fruit to be extremely different among the 

 plants thus associated, and compelled the separation of the new genera, Calo- 

 pjhyllis, EhodopJiyllis, Rhizophyllis, Euthora, and Calliblepharis, wliile of those that 

 remain some belong to Gigartina, some to Gracilaria ; and of the sixteen species 

 enumerated by Dr. Greville, only five belong to the modern genus Rhodymenia ; 

 the rest dispersing into three different Orders. This example may suffice. Dr. 

 Greville's system was published in 1830. The next decided improvement in sys- 

 tem was developed in 1841-1842, by Professor J. Agardh, f who, in describing the 

 Algfe of the Mediterranean and Adriatic, took occasion to reform the generic charac- 

 ters, by introducing into the diagnosis the internal structure of the frond, and by 

 more accurately describing the fructification. Much remained still to be accom- 

 plished, and new genera founded on the reformed principles were added by Mon- 

 tague and others. In 1843 Kiitzing published his " Fhycologia Generalis,"^ accom- 

 panied by eighty anatomical plates of unrivalled excellence and beauty. In this 

 great work many new genera were defined and illustrated, and a new system of 

 distribution was proposed. The chief excellencies of the book are its anatomical 

 illustrations : its faults are, the needless alteration of established names ; the intro- 

 duction of unnecessary glossology ; and the multiplication of Orders, genera, and 



Char, essent. Fructus uniformis : capsiilfe glomerulum seminum minutissimornm sphsericum 

 includentes. 



t J. Ag. Symbokv in Linnjca XV. p. 1 (1841). J. Ag. "Alga; maris Mediterranei et Adriatici obser- 

 vationes in diagnosin spccierum, et dispositionem generum." Paris, 1842. 



t "Pbycologia Generalis, oder Anatomie, Physiologie, iind Systemkunde der Tange." Leipsig, 1843. 



