i88 



THE ALGAE 



months or more). Their form is determined by nutrient supply, 

 bacterial growth, temperature, etc., leading to presence or absence 

 of sex organs, extreme branching or very compact branching. The 

 ova are normally fertilized in the sea, and though occasionally a 

 single ovum may be fertiUzed whilst still in the oogonium, this can 

 only be regarded as an abnormality. 



EcKLONiACEAE : EckloTiia (after Ecklon). Fig. 107 



This is a southern hemisphere genus. There is a short, soUd un- 

 branched stipe which is attached to the rocks by means of the usual 

 rhizoids. In the young plant the stipe expands into a flatenned 



Fig. 107 Ecklonia radiatay young, juvenile and adult plants ( x J). 



(After Bergquist.) 



frond which is initially dentate. Later the terminal portion disap- 

 pears and the basal portion produces numerous lateral outgrowths 

 (sporophylls). In its internal morphology the structure is compar- 

 able to that described for Laminaria. 



Alariaceae: Alaria (ala, wing). Fig. 108 



This genus is widely distributed throughout the northern hemi- 

 sphere, the common species being A. esculenta. There is a short, 



