Algals.] 



CERAMIACE.E. 



23 



ORDER IV. CERAMIACE^E.— RosETANGLEs. 



FiiORiDEvE. J. Ayardh, Alg. Med. 54. (1842) ; Endl. Gen. Supp, iii. 33. — Choristospore^, Decaisw in 

 Ann. Nat. Hist. 2 ser. 17, 306. (1842). 



Diagnosis. — Cellular or tubular umymmetrical bodies, multiplied by tetraspores. 

 Seaweeds of a rose or purplish colour, seldom olive or violet. Their cells long and 

 tubular, or round and short, or polygonal ; sometimes aiTanged in a single row ; some- 

 times disposed in several parallel rows, and 

 of equal length, forming an articulated frond ; 

 sometimes in several rows, and of unequal 

 length, when they constitute a cellular frond. 

 The propagation by means of spores (called 

 also Sphserospores and Tetraspores), formed 

 in fours (or threes), ^\-ithin a transparent peri- 

 spore, or mother cell, and collected in bodies 

 of many different forms and structui'e.* 



The subdix-ision of the reproductive bodies 

 or tetraspores into four, or occasionally three 

 particles, is the great feature of this natural 

 order, and at once distinguishes it from the 

 rest of the alhance. M. Decaisne lays great 

 stress upon this point, first used by himself 

 for systematical purposes, and he attaches 

 quite a secondary value to the various modes 

 in which such spores are grouped. To rank 

 those modes more highly c'etait sacrifier evi- 

 demment une foule des considerations de la 

 plus haute valeur a. un caractere qui n^a d' autre importance que d'etre plus visible, et par 

 suite plus facile a saisir que le premier. It is, however, a very striking pecuharity of 

 the Rosetangles, that they should have so much greater a variety of fructification 

 than their aUies, and this, in connection with the quaternary structure of their spores, 

 seems to indicate their bemg the highest form of the Algal alhance. 



Although the subdixdsion of the spores ^ 



by four is of unifoinn occurrence among 

 these plants, yet it takes place in different 

 ways, and is subject to certain modifica- 

 tions, concerning wliicli the language of ^I. 

 Decaisne is instructive. " I have she«-n," 

 he says, " in another place, that the sphaero- 

 spores, or quaternary reproductive bodies, 

 wliich M. KUtzing has perhaps better 

 called Tetraspores, offer three modifica- 

 tions. They are either little spheres, 

 which dixdde into four wedge-shaped par- 

 ticles with a round base (Delesseria, Ce- 

 ramium, &c.) ; or oVjlong bodies, wliich 

 are cut across into four distinct spores 

 (Hypnea, Catenella, &c,) ; or, finally, ob- 

 long bodies, which divide vertically and 

 transversely, so as to fomi segments of 

 cylinders, rounded at one extremity, and 

 truncate at the other, as m PeysonneUa. 

 The mode of formation, and the essential 

 organisation of these spores, is the same 

 in each type, whether the tetraspores pro- 

 ject beyond the tissue, or are organised in 

 the interior of the frond. When young, 

 the tetraspores show no exterior mem- 

 brane, but appear as a reddish spherule, 

 the development of which may be followed 



Fig. XI. 



* For the explanation of the terms invented to express these forms, see Decaisne in Ann. des Sc. Nat. 

 2 ser. 17, 348. 



Fig. X.— 1. Chondria obtusa ; 2 Griffithsia sphserica ; 3. Gr. corallina. 



Fig. XI.— Magnified branch of C'orallina officinalis ; 2. a section of its spore case (ceramidmm) with 

 the tetraspores in situ ; 3. a tetraspore ; 4. Cymopolia barbata ; 5. a cross section of the stem of Dasy- 

 cladus clavaeformis, showing its rings of gro^vth. 



