224 



RHODOPHYCEAE 



composed of several carpogonia together with nutrient cells, and 

 more than one of these carpogonia may be fertilized. The genus is 

 the principal source of agar-agar, a gelatinous medium much used 

 in mycology and bacteriology, in the manu- 

 facture of size and in culinary operations. 

 Agar-agar is manufactured primarily in -*^ ^^ 



Japan where it possesses various names, 

 Kanten, Japanese, Bengal or Oriental isin- 

 glass, and Ceylon or Chinese moss. The 

 plants contain about 76 % of the primary V^ 

 gelatinous material, gelose, and are dived ^^^ 

 for between May and October, after which 

 they are allowed to dry and bleach in the 

 open, and then they are sold to factories up 

 in the mountains where the air is pure, 

 dry and cold. Here the alga is cleaned, Fig. 147. Gelidiumcorneum. 

 drained and fused into sheets and the (After Oltmanns.) 

 jelly extracted by boiling. After straining, the jelly is poured into 

 wooden trays and allowed to cool and then it is cut into bars. In 

 former times the algae were just simply dried in the sun and the 

 jelly extracted afterwards by boiling. 



CR YPTONEMIALES 



*DuMONTiACEAE : Dudresuaya (after Dudresnay de St-Pol-de-Leon). 

 Fig. 148. 

 The cylindrical, much-branched thallus is soft and gelatinous, 

 consisting when young of a simple articulated filamentous axis with 

 whorls of dichotomously branched ramuli, although in older plants 

 the central axis becomes polysiphonous and clothed with densely 

 set whorls of branches. The plants are dioecious, the males being 

 somewhat smaller, paler and fewer in number than the females. 

 The carpogonial branches of D, coccinea arise from the lower cells 

 of short side branches and when fully developed are composed of 

 seven to nine cells : they are branched once or twice and may have 

 short sterile side branches arising from the lowest cell. In the middle 

 of the mature carpogonial branch there are two to three larger cells 

 which function in a purely nutritive capacity, whilst the auxiliary 

 cells develop in similar positions on neighbouring branches that 



