lyO THE ALGAE 



tained by an intercalary growing zone some way behind the apex. 

 Since the estabhshment of the Hfe history of the genus it has been 

 removed from the Ectocarpales into a separate order. 



REFERENCE 



Fritsch, F. E. (1945). Structure and Reproduction of the Algae, Vol. II, 

 pp. 180-91. Camb. Univ. Press. 



* Laminariales 



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. 



There is considerable variation in habit between the sporophytes 

 of the different genera. They range from the long whip-Uke thallus 

 of Chorda (Fig. 96) to the enormous giant Macrocystis (Fig. 106). 

 In between these extremes are found the sea palm, Postelsia (Fig. 

 104), and the sea fern, Thalassiophyllum (Fig. 102). In the northern 

 hemisphere Laminaria is a typical representative of the genus and 

 Ecklonia in the southern whilst Macrocystis is a useful teaching 

 representative in the Pacific and in South Africa. 



The genera Saccorhiza and Alaria are of great interest because 

 the fronds possess shallow conceptacles or cryptostomata that re- 

 semble those found in the Fucales, those in the first-named genus 

 even possessing the typical tuft of hairs. This does not necessarily 

 mean that either of these two genera could be a source of origin for 

 the Fucales, and indeed it is Hkely that such conceptacles have 

 arisen more than once in the course of evolution. 



