1919] Setchell-Gardner : Myxophyceae 45 



12. Radaisia Sauv. 



Plants formino; small, compact masses of cells on the surface of 

 the host, consisting of a more or less parenchj-matous basal layer 

 formed by repeated divisions in vertical planes of a single cell, and 

 of simple or complex, erect, more or less branched filaments arising 

 from the basal layer by horizontal divisions and usually very com- 

 pact and more or less coalcscent; gonidangia arising by modification 

 of terminal cells of the erect filaments. 



Sauvageau, Sur le Radaisk, 1895, p. 373 (p. 2, Repr.), pi. 7, fig. 1. 



The genus Radaisia vv^as founded hy Sauvageau {loc. cit.) to 

 receive two species, R. Gmnontiana Sauv. and R. Cornuana Sauv., of 

 which the first, both because of its position in the article and because 

 it is described and figured with gonidangia, may be taken as the type. 

 It is a marine species, epiphytic upon species of Fucks, and was found 

 in the southwest of France, at Biarritz and at Guethary. 



The type shows a minute cushion, composed of vertical and slightly 

 radiating filaments which are simple or occasionally fastigiately dicho- 

 tomously branched, whose terminal cells are transformed into large, 

 spherical, ovoid or pyriform gonidangia. Of the development, and 

 manner of the cell divisions Sauvageau says nothing. The second 

 species is an inhabitant of fresh water, growing on submerged stones 

 in rapidly flowing springs, but was not provided with gonidangia. 



From the figures and description of the adult stages of Radaism 

 Gomontiana and from the study of our R. Laminariae, which seems 

 certainly to be referred to the same genus, it appears that the divisions 

 of the cells take place variously and successively in one, two, and three 

 directions. Apparently a cushion may and does arise, as a rule, from 

 a single cell (gonidium). By divisions taking place in two directions, 

 perpendicular to the substratum, a layer of cells is formed. The cells 

 of this layer divide, after a time, in the third direction, i.e., parallel 

 to the substratum, producing the filaments which form a cushion out 

 of the layer. The filaments by occasional division in other directions 

 than parallel to the substratum initiate branches and consequently 

 the radiate structure of the cushion arises. The transformation of the 

 terminal cells into large and conspicuous gonidangia completes the 

 structure of the typical species. 



We have followed the distinction set forth by Gardner (1918, 

 p. 432) in distinguishing Rad-aisia from Hyella. Rad-aisM, then, will 

 include those forms with erect filaments, simple or complex, closely 



