484 SUMMARY OF CURRENT RESEARCHES RELATING TO 



largest prothallia attain a diameter of about 1 mm. ; their long cells are 

 5 /J. wide ; the short cells, which have become torulose, are 6-10 /a wide. 

 Each possesses one or two chromatophores, a nucleus, one or two droplets 

 of oil, and some very small globules of fucosan. At the end of February 

 appeared narrow plurilocular gametangia, cylindrical, obtuse, preferably 

 on the torulose cells. They are composed of two to twelve uniseriate 

 locules, often three or four, the lower one sometimes belonging to the 

 filament itself. Each locule encloses a single gamete, with superior or 

 lateral chromatophore, and very distinct red spot. The walls separating 

 the locules disappear before dehiscence, and the gametes round them- 

 selves off. Dehiscence is terminal and fairly slow. The gametes, 

 scarcely differing from zoospores, measure about 6 /x by 4 /x. Thus the 

 prothallus of Dictyosiphon resembles a Strehlonema. While examining 

 the prothalli the author has often watched dehiscence. Most of the 

 gametes hardly escape from the network of filaments. An hour later 

 they come to rest, become rounded, and disaggregate. In cellular 

 cultures they move away from the window, but the small number in 

 each gametangium and their dehiscence at any hour of the day are not 

 favourable factors for the observation of fecundation. Some are de- 

 stroyed, others, parthenogenetic, become enclosed in a membrane, and 

 then measure 4 /a. Among the latter, certain rounded globules, rather 

 larger and possessing a nucleus, two chromatophores and two red spots, 

 can be nothing but zygotes ; isogamy takes place, no doubt, as in Ecto- 

 carpus siliculosus, between a stationary and a motile gamete. 



The germination of the zygotes and the parthenogenetic gametes, 

 preceded by an increase of diameter which soon prevents the distinguish- 

 ing of one from the other, takes place shortly. A creeping filament is 

 emitted, and, at the extremity of the same diameter, a long colourless 

 erect hair. The filament elongates, branches, produces hairs, and 

 resembles a small prothallus. Towards the end of April, certain cells 

 divide, and produce a small projecting piliferous mass which soon takes 

 the form of a narrow pyramid of cells with external rounded wall. 

 When this pyramid reaches 100-150 /x its uniseriate summit elongates 

 by means of its terminal cell, and shows the characteristic division of 

 Dictyosiphon. The germination of the zygotes on the parthenogenetic 

 gametes provides therefore a protonema, which bears plantlets. The 

 cycle of vegetation of Lammaria round our coasts comprises a hetero- 

 gamous dioecious gametophyte, and a sporophyte or true Laminaria. 

 That of Didyosiphon comprises an isogamous gametophyte, probably 

 monoecious, a microscopic protonema, and a sporophyte or true Dictyo- 

 siphon. Nothing similar has been recorded for the Brown Algae. 



Dumontia filiformis.* — G. A. Dunn has made a special study of 

 Dumontia filiformis which she found at South Harpswell, Maine, in 1913. 

 She describes the plant fully in all details, externally and internally, and 

 finally summarizes her results, for which in full the original paper must 

 be consulted. The vegetative structure is of a type occurring in many 

 families of the Floridese. Growth is apical throughout the entire thallus. 



* Bot. Gaz., Ixiii. (1917) pp. 425-67 (4 pis.). 



