128 THE ALGAE 



should be reserved for plants that are diploid and which have arisen 

 from diploid swarmers produced in plurilocular sporangia on the 

 macroscopic plants. Such plethysmothaUi can then be regarded as 

 diploid sporophytes which have been indefinitely arrested at the 

 ectocarpoid stage. Since some of the so-called protonema may also 

 bear plurilocular sporangia it would seem that the various cate- 

 gories cannot be sharply distinguished and their systematic useful- 

 ness, especially that of the protonema, is thereby diminished. 



REFERENCES 



Church, A. H. (1920). Somatic organisation of the Phaeophyceae, Oxf. 



Bot. Mem.} No. 10. 

 Fritschj F. E. (1945). Structure and Reproduction of the Algae, Vol. II, 



pp. 19-42. Camb. Univ. Press. 

 Kylin, H. (1933). Lunds Univ. Arsskv., N.F., Avd. 2, 29, No. 7. 

 Papenfuss, G. (1951). Manual of Phycologyy pp. 1 19-158. Chron. Bot. Co., 



Waltham, Mass. 



* ECTOCARPALES 



The members of this order, which are the least specialized of the 

 Phaeophyceae, exhibit some range of form, but fundamentally they 

 are of filamentous construction and basically are heterotrichous 

 with prostrate and erect portions of the thallus, though one or other 

 may subsequently become lost. A nimiber represent forms that 

 have become reduced as a result of either an epiphytic or para- 

 sitic habit. 



* EcTOCARPACEAE : Ectocarpus (ecto, external; carpus, fruit). Fig. 70 



The plants are composed of uniseriate filaments which are 

 sparsely or profusely branched. The aerial portion is sometimes 

 decumbent and arises from a rhizoidal base, which in some of the 

 epiphytic species occasionally penetrates the host, and it is also pos- 

 sible that there may be one or two examples of mild parasitism. 

 E. fasciculatus grows on the fins of certain fish in Sweden, but the 

 nature of the relationship in this case is not clear. The branches of 

 some species terminate in a colourless mucilage hair: in young 

 plants of £. siliculosus these hairs are quite long, but later, with in- 



