192 PHAEOPHYCEAE 



as the genus is dioecious, occur over the whole of the lamina, this 

 condition being regarded as the primitive state for the Fucales. It is 

 known as the *'bull kelp" and forms submarine forests in deep 

 waters off New Zealand and the Aucklands down to depths of 

 30 ft., or else it grows in places continually exposed to surf. 



FUCO-ASCOPHYLLAE 



*Fucaceae: F«cw5 (a seaweed). Figs. 129-13 1. 



This genus contains a number of species that are widely scattered 

 over the world with the majority in the northern hemisphere, 

 many of them exhibiting a wide range of form with numerous so- 

 called varieties. When two or more species occur in the same area 

 they are generally present in different zones on the shore, probably 

 dependent upon the degree of desiccation that they can tolerate 

 (cf. p. 353). The plants are attached by means of a basal disk and 

 there is usually a short stalk, which continues on to form the 

 mid-rib of the frond in those regions where the expanded wings or 

 alae are developed, these latter being of varying width with either 

 entire or serrate margins. Branching is commonly dichotomous or 

 subpinnate, and in many species the branches bear expanded 

 vesicles or pneumatocysts . Sometimes whole portions of the frond 

 may be inflated in an irregular manner, but the factors causing this 

 phenomenon are not known, although it is possible that contact with 

 rock or soil provides the necessary stimulus. With increasing age the 

 lower portions of the alae may be frayed off by wave action, leaving 

 only the mid-rib, which then has the appearance of a stipe. The 

 whole of the expanded thallus is covered with sterile pits or crypto- 

 stomata similar to those of Saccorhiza, but in fruiting plants it is 

 only the ends of the branches that become swollen and studded 

 with the fertile conceptacles. In F. spiralis these conceptacles are 

 hermaphrodite, containing both mega- and microsporangia ; in 

 F. vesiculosus and F. serratus the plants are dioecious, the two types 

 of sporangia occurring on separate plants, whilst in F. ceranoides 

 either state may be found. A number of very peculiar forms have 

 been described which commonly occur on salt marshes: these 

 rarely fruit, reproduction being secured principally by means of 

 vegetative proliferations (cf. p. 325). The age of Fucus plants has 



