448 SYSTEMATIC BOTANY. 



groups Fucoideae and Confervoideae of Harvey and others, with which they 

 are usually placed parallel. The character of the spores seems to be the same 

 throughout, although the fruits in which they are contained offer several 

 successive degrees of complexity : the favdlce of Ceramiece, and ihefavel- 

 lidia ofCryptonemie.ee, immersed or superficial groups of spores surrounded 

 by a hyaline coat the coccidia of Delesseriece, hollow cases with thick 

 membranous walls, containing a dense tuft of spores arising from a 

 central peduncle and the ceramidia of Pohfsiphonia &c., ovate or urn- 

 shaped cases with thin and membranous walls, having a tuft of spores at 

 the base all these are but slight modifications of one (the conceptacular) 

 kind of fruit, which produces the true spares. The various modes of 

 arrangement of the tetraspores (which appear from Pringsheim's observa- 

 tions to be gonidia, or gemmulary bodies, since they grow up at once into 

 a new thallus, while the other spores do not) the scattered arrangement, 

 the sori or definite groups, and the stichidia or metamorphosed branches 

 enclosing tetraspores, have a like relation ; and an analogous relation runs 

 through the modes of arrangement of the antheridia, which, it may be 

 mentioned, are rarely found in the same individuals of the species as the 

 spores. The antheridia discharge minute spherical corpuscles, to which 

 the best observers deny the power of spontaneous motion, as is the case in 

 regard to the spermatia of Lichens and Fungi ; but they are generally 

 supposed to have a fertiliring function. The simpler forms of thallus 

 occurring in this Order relate it to Ulvece and Confer voidece, while the 

 existence of tetraspores, globular spores, and antheridia in the Dictyotaceae 

 makes that Order form a direct transition to the Fucacese. The mode of 

 fertilization, by means of the antherozoids and the trichogyne, is de- 

 scribed under the head of Reproduction, p. 439. 



Distribution. The Red Seaweeds are generally diffused, but diminish 

 from warm temperate latitudes both to the equator and the poles. They 

 occur in deeper water than the Olive Seaweeds, and below tide-marks, 

 flourishing best in quiet bays. 



Qualities and Uses. The abundant gelatinous or horny substance of 

 the thallus of many kinds, composed of a modification of cellulose related 

 to gum and starch, renders them nutritious : Chondrus crispus is the 

 " Carrageen " or Irish Moss ; Rhod.ymenia palmata, Iridcea edulis, and 

 other plants of the Order yield a similar excellent jelly when boiled. 

 Plocaria tenax is largely used by the Chinese for making glue. Some 

 have pungent qualities, as Laurencia pinnatifida, called " Pepper-dulse." 

 Plocaria Helminthochorton, Corsican Moss, has the reputation of being 

 anthelmintic. The Corallinece, including common Corallines (Corallina 

 officinalis) and " Nullipores " (Melobesici) , long supposed to be of animal 

 nature, are very curious on account of their complete interpenetration by 

 carbonate of lime, giving them a brittle and sometimes stony character. 



DICTYOTACE^B are olive-coloured Seaweeds with a continuous thallus, 

 bearing the reproductive organs in definite groups or lines (sori} upon 

 the surface the spores, tetraspores, and antheridia being all developed 

 in an analogous manner from the cortical layer, bursting through its 

 cuticular pellicle. This small Order is included by Decaisne in the 

 Section Laminariece of the Tribe Aplospor^fe, but has been shown^ by 

 Thuret to be quite distinct from the other Olive-coloured Seaweeds ; it is 



