134 PHAEOPHYCEAE 



in size, the smallest being the antheridia and the largest, or mega- 

 sporangia, the oogonia. The contents of the larger megasporangia 

 are sometimes capable of parthenogenetic development, when they 

 must be regarded as incipient or degenerate ova. In E. Padinae 

 the unilocular sporangia are absent and there are three kinds of 

 plurilocular sporangia. One type, which has very small loculi, 

 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 

 meiosporangia may be haploid and the megasporangia diploid in 

 character, but no cytological data appear to be available. In 

 E. vtrescens unilocular sporangia are absent and there are only 

 meio- and megasporangia, both of which always occur on separate 

 individuals. No fusion between zooids from the 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 represent a case of apogamy in which sex has been lost, 

 or it may represent 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 unknown. 

 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 directly 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 unable to find any such dwarf plants. 



A schema illustrating these features is seen in fig. 90. It has been 

 suggested that the differences between the plants from the two 

 localities are due to differences in the tides, light conditions or 



