181 



named species. The genus Cruoria, to which the species of Lyngbye was referred 

 in 1835 by Fries, was also very ill defined. Areschoug and the later authors, how- 

 ever, have applied the name of Lyngbye and Fries to the species here treated of, 

 and it must be used in the future in the same sense, as the specific name of Lyngbye 

 in fact comprises both species. 



This species, in habit quite resembling Petrocelis Hennedyi, forms crusts on 

 the stems of Laminaria hgperborea, stones, shells of Mytiliis and barnacles, more 



rarely on Fncus serratus and 

 the basal part of Halidrys 

 siliquosa, from 1 to 12 cm in 

 diameter or more. The crust 

 has at first a basal layer con- 

 sisting of one layer of cells 

 y ^C3) Jl R // / f''0'n which the vertical fila- 



^^C^ jfy^^%j^/i/f] ments are given off. The fila- 



Fig. 100. Fig. 101. 



Cruoria pellita. A. border of frond seen from above. B, verlical section Cruoria pellita. Basal layer of frond seen 



of under part af frond showing basal layer and sub-basal layer. C, sinii- from the under face, showing creeping 

 lar, older crust. 390:1. C 230:1. rhizoidal filaments. 390:1. 



ments of the basal layer are radiating towards the margin (fig. 100 A). According 

 to ScHMiTz and Hauptfleisch (1897, p. 535) the thallus is quite coalesced with the 

 substratum and without root-hairs ( Wurzelhaare) ; the first is true, but the latter 

 assertion is not quite correct. As shown in figs. 100 and 101, short filaments are 

 here and there given off" from the under side of the basal layer; these filaments 

 have first the character of unicellular rhizoids, but increase in length and form 

 long septate filaments running under the primary basal layer, and in older crusts 

 they may form a continuous layer consisting of one to more layers of variously 

 disposed cells, the undermost of which may have the character of rhizoids pene- 

 trating into the unevennesses of the substratum, while the upper cells in thicker 

 fronds resemble those of the primary basal layer. According to Schmitz and Haupt- 

 fleisch (1. c), rhizoids are frequently produced in the undermost part of the cor- 

 tical layer. 



