EUPHYCOPHYTA 63 



separated from each other by vacuoles, although occasionally they 

 may come together to form a diffuse net-work. Each disc normally 

 possesses one or two nuclei. In most of the species the septa 

 develop as ingrowths, though in vS. africana they are replaced by a 

 series of strands which sometimes fail to meet at the centre so that 

 the coenocytes are continuous. 



Vegetative reproduction is secured by means of fragmentation, 

 and there is apparently no asexual reproduction though zoospores 

 have been reported in S. wilmani: these may, however, be par- 

 thenogenetically developing ova. In sexual reproduction, although 

 the cells do not change in shape, nevertheless both oogonia and 

 antheridia are formed singly or in series, the species being either 

 monoecious or dioecious. In the formation of oogonia the annular 

 chloroplasts first become reticulate and then the ova are formed 

 without any nuclear divisions being involved. In 5. annulina the 

 ova are non-motile, but in S. camhrica the large female gametes are 

 biflagellate, thus representing an advanced anisogamy. In the an- 

 theridia the nuclei do undergo division and numerous, elongated, 

 narrow antherozoids are formed which are liberated through small 

 pores, subsequently penetrating the oogonial cells through similar 

 perforations. The fertilized ovum {oospore) becomes surroimded by 

 a hyaHne membrane, and then inside this two new membranes are 

 laid down, after which the first one disappears. The new external 

 membrane is ornamented and the contents become a brick red. 

 Germination stages are only known for some species and the 

 oospores lie dormant for several months or even years. On ger- 

 mination 1-4 biflagellate swarmers (8 occasionally) are normally 

 produced which come to rest and then grow into new plants. 

 Sometimes the swarmers do not separate and so one gets a four- or 

 eight-flagellate synzoospore depending on whether it comprises two 

 or four zoids. These develop to a four-fold sporeling or sporeUng 

 with four claws. In some cases the swarmers from the oospore are 

 completely suppressed and a new filament develops directly (cf. 

 Fig. 34), this type of reproduction being known as azoosporic. In 

 the most complete life cycle investigated the motile ova may also 

 develop parthenogenetically after forming a short non-motile 

 structure which divides to produce three new filaments. Various 

 reduction stages from this life cycle can be noted among the differ- 

 ent species (cf. Fig. 34). The adult plants are haploid because 

 meiosis is known to take place at the segmentation of the oospore. 



