FUCALES (HETEROGENERATAE) 



199 



otherwise absent from the genus. The sporangia are similar to those 

 of Fucus except that normally only two ova mature, the remaining 

 six nuclei being extruded from the cytoplasm into the wall, though 

 in Pelvetia fastigiata one may occasionally find four ripe ova or else 

 ova that contain two nuclei. In P. canaliculata the two mature eggs 

 are arranged one above the other, whilst in the Japanese species, 

 P. Wrightiij they are placed side by side. This difference is probably 

 dependent upon the relative position of the two megaspores which 

 germinate. 



*Fucaceae: Ascophyllum (asco, wine-skin; phyllum, leaf). Fig. 133. 



The plants of this genus are large, often attaining several feet in 

 length, and are commonly to be found on sheltered coasts at about 



Fig. 133. Ascophyllum nodosum. A-C, diagram showing method of branching. 

 A, apical cell. A^-A^, secondary initials in order of development. AA^ , AA2, 

 tertiary and quaternary initials. D, plant ( x i). E, microsporangia ( x 225). 

 F, megasporangium (x2-25). (A-C, after Oltmanns; D-F, after Newton.) 



