126 THE ALGAE 



fibrils and the shorter posterior one of nine fibrils which seem to 

 be of a rather different nature. Down the sides of the long flagellum 

 can be found small hairs which presumably make it a more efficient 

 locomotory organ. 



Both unilocular and plurilocular sporangia are commonly found, 

 but the fate of their products varies considerably. Plurilocular 

 sporangia can be borne on both diploid and haploid plants, whereas 

 unilocular sporangia are commonly confined to diploid plants. The 

 plurilocular sporangia on the diploid plants represent an accessory 

 means of reproduction, whilst those of the haploid generation are 

 gametangia. In isogamous forms gametes are normally produced 

 from plurilocular sporangia, so that in anisogamous forms the 

 antheridia and oogonia must be regarded as modified plurilocular 

 sporangia. On this basis the plants can be divided into two groups 

 as in Table 2. 



Table 2 



Sporangia in Phaeophyceae 



I. One kind of plurilocular sporangium. 



(i) Uni- and plurilocular sporangia on the same individuals, e.g. 



Ectocarpus spp. 

 (ii) Uni- and plurilocular sporangia on different individuals, e.g. 

 Sphacelaria bipinnata, Cladostephus. 

 II. Two kinds of plurilocular sporangia. 



(i) Meio- and megasporangia, e.g. E. virescens (.see p. 130). 

 (ii) Micro- and megasporangia : 



{a) Unilocular sporangia only on separate plants, e.g. Sphace- 

 laria hystrix, Halopteris filicina. 

 (b) Unilocular sporangia and both types of gametangia all on 

 separate plants, e.g. Sphacelaria harveyana. 

 (iii) Antheridia and oogonia : 



{a) Unilocular sporangia on separate plants, e.g. Halopteris 



hordacea, Dictyota, Laminaria. 

 (b) Unilocular sporangia absent, e.g. Fucales. 



In general the presence of a unilocular or tetrasporic sporangiimi 

 indicates a diploid thallus, and as reduction division occurs in the 

 formation of the contents the swarmers are invariably haploid. A 

 haploid zooid, irrespective of whether it comes from a pluri- or 

 unilocular sporangium can behave either as a gamete or as an 



