THALLOPHYTA: ALGAE 



79 



Other Kelps. As in Laminaria, the bodies of nearly all the other kelps 

 are differentiated into holdfast organs, stout stalks, and flat blades often 

 much divided into narrow segments. Air bladders are freciuently present. 

 Reproduction is similar in all members of the order. The greatest variety 

 and largest of the kelps occur along 

 the Pacific coast of North America, 

 where they live in water 10 to 30 m. 

 deep, their stalks attached to rocky 

 reefs and their blades often floating 

 on the surface. Macrocijstis may 

 reach a length of 30 to 50 m. A sin- 

 gle plant consists of a stalk with 

 many blades, each blade having a 

 float (Fig. 66). Another large kelp 

 is Nereocijstis, with a large hollow 

 bulb at the end of a thick stalk and 

 a number of blades arising from the 

 bulb (Fig. 67). It reaches a length 

 of 25 to 30 m. Postelsia, known as 

 the "sea palm," has a stout stalk up 

 to 60 cm. long bearing at its tip nu- 

 merous branches terminating in nar- 

 row blades (Fig. 68). Egregia, the 

 "feather-boa kelp," has a long stalk 

 that bears two rows of lateral blades 

 and floats, the blades producing 

 sporangia being much narrower 

 than the sterile ones. 



Summary. The vegetative body 

 of the Laminariales is highly differ- 

 entiated both externally and inter- 

 nally. It consists of a massive 

 thallus usually with a holdfast, stipe, 

 and one or more blades. Growth 

 is due to an intercalary meristem. 

 The large plant body is a sporo- 

 phyte bearing unicellular sporangia 

 that contain many zoospores. The 

 gametophytes are microscopic, dioecious, and heterogamous. The sperms 

 are biciliate and produced singly in unicellular antheridia. The eggs are 

 nonmotile and borne in unicellular oogonia. The Laminariales have a 

 heteromorphic alternation of generations. 



Fig. 67. Young plant of Nereocystis 

 luetkeana, one-quarter natural size. 



