132 PHAEOPHYCEAE 



sporangia. Until recently these were regarded as arrested sporo- 

 phytes in a juvenile condition. 



Fritsch, however, has suggested (1939) that some of these plethys- 

 mothalli are really potential gametophytes (prothalli), especially 

 those dwarf plants which perpetuate themselves by means of 

 plurilocular sporangia. The term '^plethysmothallus" should be 

 reserved for plants that are diploid and which have arisen from 

 diploid swarmers produced in plurilocular sporangia on the 

 macroscopic plants. It has been suggested that this type of alterna- 

 tion should be termed an alternation of vegetation growths rather 

 than an alternation of generations, but it is also equally satisfactory 

 to regard it as heteromorphic alternation. 



REFERENCES 



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



Bot. Mem. no. 10. 

 Fritsch, F. E. (1939). Bot. Notiser, p. 125. 

 Kylin, H. (1933). Lunds Univ. Arsskr. N.F., Avd. 2, 29, no. 7. 

 Taylor, W. R. (1922). Bot. Gaz. 74, 431. 

 Williams, J. Lloyd (1925). Rep. Brit. Ass. Pres. Address, Sect. K, p. 182. 



ECTOCARPALES 

 (ISOGENERATAE AND HETEROGENERATAE) 



*EcTOCARPACEAE : Ectocavpus {ecto, external; carpus, fruit). Figs. 

 89, 90. 



The plants are composed of uniseriate filaments which are 

 sparsely or profusely branched. The erect 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 

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

 E. fasciculatiis even 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 E. siliculosus these hairs are quite long, but later, with 

 increasing age, they become much shorter through truncation. The 

 erect filaments have an intercalary growing region, but the 

 rhizoids increase in length by means of apical growth. Each cell, 

 which contains one nucleus together with brown disk or band- 

 shaped chromatophores, possesses a wall that is composed of three 

 pectic-cellulose layers. 



