130 THE ALGAE 



weaker gamete behaving as the opposite sex towards the younger 

 and stronger gamete. 



In Gijfordia secunda {E. secundus) there is well-marked aniso- 

 gamy, as seen by the two types of plurilocular sporangia with large 

 or small locuH that produce zooids which differ in size, the smaller 

 gametangia being the antheridia and the larger, the oogonia. In 

 addition, there is an accessory asexual plurilocular sporangium or 

 meiosporangium. The contents of the oogonia are sometimes cap- 

 able of parthenogenetic development. In E. padinae the unilocular 

 sporangia are absent and there are three kinds of plurilocular 

 sporangia. One type, which has very small locuH, represents the 

 antheridia, whilst there are also medium-sized or meiosporangia, 

 and large or megasporangia. The latter probably represent the 

 female reproductive organs, but there is, at present, no definite 

 proof for this hypothesis. It has been suggested that the meiospor- 

 angia may be haploid and the megasporangia diploid in character, 

 but no cytological data appear to be available. In E. virescens uni- 

 locular sporangia are present together with meio- and megaspor- 

 angia, both of which always occur on separate individuals. No 

 fusion between zooids from the last two types of sporangia has been 

 observed, but the zooids of the megasporangia are not very mobile 

 and frequently germinate inside the sporangium. This may repre- 

 sent a case of apogamy in which sex has been lost, or it may repre- 

 sent parthenogenetic development of ova because the male organs 

 (the meiosporangia) have ceased to function. In any case it must be 

 regarded as a type in which some degeneration has occurred. 



The life cycles of the species are full of interest, especially in view 

 of what has been discovered for E. siliculosus. Knight (1929) found 

 that the plants in the Isle of Man occurred in early spring and late 

 autumn and were all diploid, the haploid generation being un- 

 known. They bore unilocular and plurilocular sporangia, the former 

 producing gametes after a reduction division whilst the latter gave 

 rise to zoospores. In the Bay of Naples, on the other hand, the large 

 plants were all haploid and only bore plurilocular sporangia. The 

 zooids from these behaved as gametes, and after fusion meiosis 

 commonly took place when the zygote commenced to germinate 

 because it normally developed direcdy into a new haploid plant. 

 Berthold recorded a microscopic form which has since been re- 

 garded as diploid because unilocular sporangia were found on it, 

 but Knight was imable to find any such dwarf plants. 



