SETCHELL— PARASITISM AMONG RED ALG^. 169 



oblique divisions and as this continues the contents of a tetrasporan- 

 gium act as a whole, producing penetrating rhizoidal filaments below 

 and a regular, though much dwarfed, AgardhicUa-irond above. The 

 rhizoidal filaments penetrate even into the region of the medullary 

 hyphse of the parent plant and establish " secondary connections " 

 with them. There seems certainly to be here a parasitic red alga 

 in the making. There exist full-sized plants of Agardhiella tenera 

 of all three sorts, viz., antheridial, cystocarpic and tetrasporangial. 

 There exist also dwarf plants, parasitic on, but arising from, the 

 tetrasporangial plant. While these dwarf plants, and they are very 

 much reduced and simple, are largely antheridial, yet, according to 

 Osterhout,, all three kinds of dwarf plants, viz., antheridial, cystocar- 

 pic and tetrasporangial, may exist side by side, all parasitic on and 

 probably arising from the same full-sized tetrasporangial plant. In 

 order that our knowledge of this interesting and seemingly very sig- 

 nificant case may be more complete, it is very desirable that culture 

 be made from the spores (both carpospores and tetraspores, if ob- 

 tainable) of the dwarf plants. It is very desirable that this be 

 undertaken by some investigator who has access to abundant growths 

 of these plants. The very similar species, Agardhiella Coiilteri 

 (Harv.) Setchell, of the California coast has not been observed to 

 produce dwarf plants (or bristly proliferations) from the tetra- 

 sporangial generation. 



In summarizing, then, the aim of this paper, it may be said to 

 be intended to indicate how general is the extent of the parasitism 

 of the parasitic genera and species of red algse upon their near rela- 

 tives and to draw attention to the similarity of these cases and the 

 case of the production of a dwarf parasitic generation from the 

 tetrasporangia of Agardhiella tcncra and with the hope of suggesting 

 the probability of their origin. 



Bibliography. 



Batters, E. A. L. 1892. Gonimophyllum Buffhami : A New Marine Alga. 

 Journ. of Botany, Vol. 30, pp. 65-67, PI. 319. 

 1895. On Some New British Marine Algge. Annals of Botany, Vol. 9, 



PP- 307-321, PI. II. 

 1902. A Catalogue of the British Marine Algse. Suppl. Journal of 

 Botany, Vol. 40, pp. 1-107. 

 Bornet, Ed. 1878. Consult Thuret et Bornet, 1878. 



