334 TRR JOUKNAL OF BOTANY 



of a cystooarpic ivall^ without or with the differentiation of an ostioU 

 after fertihzation, passing on to the initiation of these structui-es 

 before fertihzation (in the special case of the ceramidium), Represents 

 a sev^juence of morphological specialization of a significance fully equal 

 to tliat of the parasitic connection by secondar^^-pits and nuclear 

 migi-ation, as new departures in the race. A true phylogenetic 

 classification should thus combine — (1) the ' auxiliary cell' standpoint 

 of Schmitz, with (2) the special features of thallus-organization, 

 and (3) adult cystocarp-differentiation, more clearly recognized as 

 significant by the intuition of the older algologists (Harvey). And 

 though it may be convenient temporarily to attach an exaggerated 

 signiticance to one special line at one time more than to another, 

 just because it is obscure and hence less known (as in more recent 

 years cytological problems have been regarded as the sine qua noii), 

 pliylogeny takes count of all paths of progress. 



Apart from the ' general equipment ' of the Floridese as a race, 

 the ' s])ecial lines ' are for practical purposes thus reduced to three ; 

 it may be pointed out that these do not necessarily run concuri-ently ; 

 though in the more primitive types (Helminthocladieae) all are 

 simple, and in the higher types (Eu-Floridea?) all are extremely 

 elaborate (cf. PoJysiiylwnia). The three factors in order of time 

 may be defined as : — 



I. The evolution of the autotrophic vegetative soma, with differ- 

 entiated members and tissues of special function, particularly in the 

 form of corticated axial-filament types with segmenting apical cells 

 and precise diiferentiation of lateral ramuli. 



IE. Tlie germination of the zygote in situ, and its parasitic 

 attachment to the adjacent parental tissues as a drain on the paths of 

 conduction. 



III. The structural response of the gametophyte to the stimulus 

 of the parasitic carposporophyte. 



The variations expi-essed by the different combinations of phases 

 involving these factors ^ constitute the special charm of tlie Florideaj 

 as a class, far in advance of anything remotely suggested by the more 

 dominant phytobenthon of the Phieophycea? of Northern Seas, as 

 expressed more ])articula]"ly by the familiar Fucoids and Laminarians 

 of our own shores ; this being in turn but the expression of the fact 

 that the Florideaj are pre-eminently tropical in distribi:tion and 

 origin, as deiiizens of the reef-pools of warmer seas ; comparatively 

 few reach n(n-thern watei's, and these are often the last niuch-cnduring 

 relics of a warmer geological epoch. 



Thus while Boswarva's admittedly imperfect list for Plymouth 

 Sound-, before steamer traffic had fouled the water, extends to 

 147 species, the Fieroe list at the northern limit of British distri- 

 bution gives only 75 species ; and in the Arctic Sea, according to 

 Kjellman, Spitzbergen, which feels the last influence of the Gn\i- 

 stream, can show 47 species, and the Siberian seas only 11. 



^ When the respective value of these three factors can be determined, it will 

 be time to re-arrange the admittedly wholly provisional present classification. 



2 Boswarva (1887), Journal M.^B. A. i. p. 153; Borgesen (1903), Botany of 

 the Fxroes, pp. 350, 403 ; Kjellman (1883), AJgse of the Arctic Sea, p. 72. 



