SOME BRITISH SPECIES OP PH^OPHYCE^E 369 



This being the case, an examination of the basal disk was rendered 

 easy, as was also the following out of the different stages. 



The basal disk is of the usual Myrionema type, but is more 

 irregular than in most species ; the cells may be brought out very 

 clearly by staining with gentian violet." In the young plants the 

 growth is usually regular and even, but in the older parts cases 

 may be observed in which the branching is without definite order ; 

 in other instances an almost pinnate arrangement is exhibited, and 

 the outline of such thalli is markedly lobed. The cells of the older 

 parts are usually 6-10 /x wide, and are of the same length or one 

 and a half times longer, whereas the growing cells at the margin 

 are usually 25 x 7-8 /*. True dichotomy of the marginal cells 

 was not observed. 



The thallus bears the three organs mentioned by Svedelius, viz., 

 hairs, ascocysts, and sporangia. In the British material these 

 bodies agree precisely with his description, except that the 

 sporangia are usually somewhat larger, averaging 35-55 x 8-10 fi 

 instead of 30-50 x 6 /*. Sporangia of the smaller size also occur, 

 and there is every transition between the two. The sporangia are 

 typically uniseriate ; but in the case of some old plants in which 

 the first crop of spores had been liberated, a second crop of 

 sporangia appeared, many of which showed a biseriate arrange- 

 ment. These biseriate sporangia were, for the most part, of the 

 same size and form as those of the previous crop, though in one 

 or two cases they exceeded them in size. 



The development of the ascocysts and hairs agrees with that 

 described for other species of Ascocyclus : both appear early, and 

 some may be fully grown before the earliest sporangia develop. 

 In two cases stalked ascocysts were observed, and in another 

 instance an ascocyst had become septate in the upper part. Erect 

 assimilating filaments are usually absent, but in more than one 

 plant a few r of these bodies were noted. 



Ascocyclus affinis, though a sharply defined species, is thus 

 found, when an examination is made of a considerable number of 

 plants, to vary within certain limits — (1) as to the form of the 

 basal disk, (2) the size and form of the sporangia, and (3) as to 

 the presence or absence of erect filaments. 



Hecatonema globosum Batters, Cat. Brit. Mar. Alg. p. 41. 

 Ascocyclus globosa Reinke, Algenfl. p. 46 ; Atlas, p. 20, tab. 17. 

 Phycocelis globosus De Toni, Syll. Alg. vol. iii. p. 582 ; Rosenvinge, 

 I)euxi6me Mem. p. 86. Micros j)o?igi urn globosum Reinke, Alg. der 

 Kieler Brucht, 1888, p. 20. Myrionema globosa Fosl. New or Crit. 

 Norw. Alg. 1894, p. 130. 



* The best method for making preparations of this and similar alg® is 

 by using glycerine jelly that has been stained with gentian violet, as de- 

 scribed by the writer in the New Phytologist (vol. i. 1902, p. 129). In the 

 case of the present species the whole plant, after some hours, takes up the 

 violet, the ascocysts and basal disk staining most deeply. This method, 

 successful as it is with Ascocyclus affinu and many other species, is of no value 

 for other closely allied plants, which for some reason refuse to take the stain. 

 Effective staining is perhaps dependent on the presence of certain forms of 

 mucilage. 



Journal of Botany. — Vol. 45. [October, 1907.] 2 e 



