HOW TO KNOW THE SEAWEEDS 



scopic gametophyte generation. The microscopic sexual plants are 

 rarely detectable in nature and have been learned about through 

 laboratory culture studies. Thus, among the brown algae treated in 

 this account, with the exception of the orders Ectocarpales and Dictyo- 

 tales, the plants encountered in the field will be of only one genera- 

 tion, namely, the sporophyte. 



The hfe cycle of Laminaria is presented as an example of this 

 prevalent heteromorphic type of alternation in which the two genera- 

 tions are dissimilar. Fig. 10. 



sporophyte 



A 



sort of 

 unilocular 



sporan(j/a. 



6 gametophyte 



sporophyte 

 deyelopment 



ant hero- 

 joids 



us/on 



Fig. 10. Diagram of the Life Cycle of Laminaria. 



Although in the order Fucales, which contains many of our com- 

 monest rock weeds such as Fucus, Pelvetia, Ascophyllum, etc., the 

 macroscopic plant of the field is the sporophyte generation, the life 

 cycle differs markedly from that of Laminaria in the elimination of the 

 gametophyte generation. The life cycle of Fucus is diagrammed in 

 Fig. 11. Note that the number of functional eggs in the macrosporan- 

 gium is a key character which is used in step 166 of the key. 



Nothing has been said about the orders Ectocarpales and Dictyo- 

 tales in which the gametophyte plants are present and are usually 

 essentially like the sporophyte plants. At this point the student need 



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