Fig. 130 Gelidium corneum: a, plant ( x|); b, apex; c, section of 



thallus; d, carpogonial branch; e, carpospores (ca) and nutritive 



cells (nu). (a, after Oltmanns; b-e, after Kylin.) 



primary pericentral cells, with a peripheral zone of small cells with 

 interspersed hyphae. There is no true auxihary cell, but the presence 

 of nutrient cells in the vicinity of the carpogonial branch results in 

 the production of a complex structure composed of several carpo- 

 gonia with small nutrient cells in short branches, and only one of 

 these carpogonia needs to be fertiUzed. After fertihzation a single 

 gonimoblast filament initially grows out into the mass of nutritive 

 cells, but it later branches so that a number of terminal carpo- 

 sporangia are finally formed. In the Japanese G. amansit, the 

 principal source of agar (cf. p. 448), the tetraspores are shed when 

 the water temperature rises to 20° C. and the carpospores when it 

 rises to 24° C, shedding occurring each afternoon. The spores be- 

 come fixed to the rock surface after being in contact for about ten 

 minutes. The maximum temperature for germination is about 25°- 

 26° C. The sporelings can grow in brackish water and this markedly 

 affects the length of the primary rhizoids. Growth is slow at first 

 but later becomes very rapid. More than one erect shoot may arise 

 from each basal pad or the lateral buds may grow horizontally 

 giving rise to stolons from which more buds may arise. 



Cryptonemiales 

 The members of this order are very diverse in habit. A number 

 are unixiial and similar in structure to the Gelidiales, whilst others 



235 



