LAMINARIALES (HETEROGENERATAE) 167 



REFERENCES 



Dictyota. Hoyt, W. D. (1907). Bot. Gaz. 43, 383. 



Dictyota. Hoyt, W. D. (1927). Amer. jf. Bot. 14, 592. 



Taonia. Robinson, W. (1932). Ann. Bot., Land., 46, 113. 



Dictyota. Williams, J. Lloyd (1904). Ann. Bot., Lond., 18, 141, 183. 



Dictyota. Williams, J. Lloyd (1905). Ann, Bot., Lond., 19, 531. 



*LAMINARIALES {HETEROGENERATAE) 



The Laminariales form an order which is principally temperate, 

 the bulk of the species being confined to the colder waters of the 

 earth, and there are, in particular, a number of monotypic genera 

 confined to the Pacific coast of North America. The presence of 

 such genera suggests that the original centre of distribution was in 

 the Pacific waters that surround Japan and Alaska. The thallus, 

 representing the large conspicuous sporophytic generation, is 

 nearly always bilaterally symmetrical with an intercalary growing 

 zone, whilst the gametophytes are microscopic. The sporophytes 

 reproduce by means of unilocular zoosporangia, commonly formed 

 in sori with paraphyses, whilst the gametophytes reproduce by 

 means of ova and antherozoids that are borne on separate plants. 



* Chord aceae: Chorda (a string). Fig. 113. 



The long whip-like thallus, which is clothed in summer with 

 mucilage hairs, arises from a small basal disk with the growing 

 region situated just above the holdfast. The hollow fronds are 

 simple with diaphragms at intervals, the construction of the 

 thallus being essentially that of a multiseptate cable derived from 

 the Mesogloia type by further segmentation of descending hyphae to 

 form a pseudo-parenchyma. The epidermal layer is ultimately 

 clothed with sporangia, paraphyses and deciduous mucilage hairs, 

 whilst the central cells become much elongated and support the 

 filaments that go to form the diaphragm. The zoospores on germina- 

 tion give rise to small filamentous gametophytes, the male plants 

 being composed of small cells, each with two to four chloroplasts, 

 and the female of larger cells with more numerous chloroplasts. 

 The gametangia are borne laterally or terminally on short branches, 

 but the plants do not become fertile for at least 3 months after their 

 formation and they usually require 6 months. After fertilization 

 the oospore remains attached to the wall of the oogonium. The 



