136 PHAEOPHYCEAE 



temperature, with perhaps most emphasis on the last. A further 

 study of the NeapoUtan form by Schussnig and Kothbauer (1934) 

 has subsequently revealed the existence of unilocular sporangia, 

 although the products from these did not undergo fusion. The 

 results of this study do not fit in at all satisfactorily with those of 

 Knight because it will be seen that there is a considerable seasonal 

 variation (cf. fig. 90). Yet another study of this species has also been 

 carried out in America by Papenfuss (1935), and his conclusions fit 

 in fairly well with those of Schussnig and Kothbauer. It would 

 seem, therefore, that the somewhat more complex schema of these 

 later workers is probably the more correct, at any rate so far as the 

 Neapolitan form is concerned. In America the diploid plants were 

 found growing epiphytically on Chorda or Spartina and these either 

 bore pluri- or unilocular sporangia independently, or else both 

 could be found on the same thallus. The unilocular sporangia 

 occurred only in summer, whilst the plurilocular were present 

 throughout the whole year. Although the zooids from both types of 

 sporangia acted as zoospores and germinated directly, nevertheless 

 meiosis always took place in the unilocular sporangia, the zooids of 

 which developed into the sexual plants that were found growing as 

 obhgate parasites on Chordaria, in some cases the nearest asexual 

 plants being 20 miles distant. It is suggested, therefore, that 

 dependence of the sexual generation upon a particular host may be 

 rather more common than is perhaps suspected. The plants growing 

 on Chordaria were dioecious and only bore plurilocular game- 

 tangia. It must also be borne in mind that the variations in the life 

 cycles of the plants from these three localities may be due to genetic 

 differences because, although the chromosome numbers may be 

 identical, this would not exclude such a possibility. This extremely 

 large genus is now subdivided, and recently a number of new 

 genera have been established (Hamel, 1939). 



*EcTOCARPACEAE : Pylaiella (after de la Pylaie, a French botanist). 

 Figs. 91, 92. 



There is only one species, P. littoralis, and although it is said to 

 possess a number of varieties yet it is by no means certain that they 

 may not be ecological or seasonal forms because it has been shown 

 that the movement of the water can even affect the nature of the 

 branches. In general appearance the plants are very like Ecto- 



