FUCALES (HETEROGENERATAE) 207 



with about 150 species, some being dioecious whilst others are 

 monoecious. In the ripe megasporangium only one ovum reaches 

 maturity under normal conditions, though occasionally eight eggs 

 may develop. In the former case the single ovum contains all eight 

 nuclei, but only one of these grows larger and is actually fertilized. 

 This state of affairs can be interpreted as a failure on the part of 

 the megaspores and gametophytes to form cell walls, and is a 

 secondary condition due to still further reduction. In S. filipendula 

 there is no stalk to the megasporangium and so it is embedded in 

 the wall of the conceptacle. When ripe the whole megasporangium, 

 not merely the inner wall and its contents, is discharged and 

 remains just outside the ostiole attached to the conceptacle wall by 

 a long mucilaginous stalk. 



After fertilization the first divisions take place whilst the zygote 

 is still attached to the parent plant by this long stalk. In 

 S. filipendula fertile sporangia or degenerate sporangia are found 

 in some of the cryptostomata, and this fact has been taken to signify 

 that these sterile pits are abortive or juvenile conceptacles. The 

 genus is especially abundant in Australian waters, one species, 

 S. enerve, being employed in Japan as a decoration for New Year's 

 Day because, when dried, it turns green. Various species are also 

 used in the same country for food, but the chief claim to notoriety 

 in this genus is probably associated with S. nutans, the so-called 

 Sargasso weed, which from time immemorial has been found as 

 large floating masses in the Sargasso Sea near the West Indies, 

 frequent references to it being recorded in the stories of early 

 travellers to that region. At one time it was thought that plants 

 of S. natans, together with one or two other species that behave 

 similarly, were attached in the early stages, but there would now 

 seem to be good evidence that they remain floating throughout the 

 whole of their life cycle. Borgesen suggests that these perennial 

 pelagic species originally arose from attached forms such as 

 S. vulgare, S. filipendula and S. Hystrix. 



S ARGASSACEAE : Turbinaria (like a spinning top). Fig. 139. 



The dioecious sporophyte forms a cone-like bush up to 25 cm. 

 high arising from a branched holdfast. The stiff cylindrical stipe is 

 crowded with leaves which are triangular or disk-like structures 

 borne on petioles that represent the primary sterile branch of 



