320 SUMMARY OF CURRENT RESEARCHES RELATING TO 



gametophyte is erect, the sporophyte prostrate {Cutleria). (b) The two 

 generations arise from the same part of the ancestral thallus, the other 

 portion aborting {strictly homologous alternation) : (1) The two genera- 

 tions arise from the upright system (Dicti/ota) ; (2) the two generations 

 arise from the prostrate system {Zanardinia ?). (c) The sporophyte 

 arises as an intercalated stage in the life-history, due to the elaboration 

 of the zygote {antithetic alternation) : (1) The gametophyte arises from 

 the prostrate system {Coleocheete, Hepaticee) ; (2) the gametophyte' 

 arises from the erect system (Nemalionales) ; (3) the gametophyte 

 retains both the prostrate and erect systems {Batrachospermum, Musci).. 

 {d) There are two spore-producing generations, the one an intercalated 

 phase produced from the zygote, the other strictly homologous {Poly- 

 si^phonia, Griffiths ia, and other advanced Floridese). 



Galaxaura obtusata.* — M. A. Howe publishes a note on the struc- 

 tural dimorphism of sexual and tetrasporic plants of Galaxaura obtusata. 

 In the section of Galaxaura to which G. obtusata belongs, two groups- 

 have been recognized, " Camerat.fi " and " Spissai." The plants of these 

 two groups differ markedly and constantly in the structure of the cortex, 

 which consists of three layers of cells. These are described fully by the 

 author. Briefly expressed, it may be said that the two outer layers of 

 the cortex in the Cameratae are filamentous, while in the " Spissse " the 

 cortex is parenchymatous or subparenchymatous throughout. In the 

 course of a microscopic examination of specimens of Galaxaura from 

 Bermuda, Florida, and the West Indies, representing forms referred to 

 G. obtusata, it was found that some plants showed the cortex structure 

 of the " Cameratas," and others that of the " Spissse " ; and that the 

 difference in cortical structure corresponded with the difference of repro- 

 ductive organs, whether sexual or non-sexual. Plants of the " Came- 

 ratffi" structure were always tetrasporic, while those of the "Spisste" 

 structure were always antheridial or cystocarpic. This held good for 

 all plants in all the collections examined. The author believes that na 

 such constant and pronounced dimorphism in the purely vegetative 

 microscopic structure of sexual and tetrasporic plants has ever been 

 recorded in Rhodophyceae. A sexual plant may thus be distinguished 

 from a tetrasporic one, even though apparently sterile. 



Fossil Lithothamnium.t— C. Samsonoff Aruffo describes a new 

 species of Lithothamninrii from the Post-pliocene of Brindisi. It occurs 

 sometimes in the form of a crust, and sometimes (more often) as a 

 ramifying form. The alga forms crusts of about a millimetre thick 

 round shells of TurritelJa, making a model of the shape. The crusts are 

 not stratified or zoned, and are often superposed. More often the alga 

 is branched, the branches being short and thick, sometimes noduliform,. 

 with frequent bifurcations. The tips of the branches are often swollen 

 and clavate, rounded, never acuminate. The habit of the alga is- 

 difficult to determine, owing to its great friability, but it appears that 



* Bull. Torrey Bot. Club, xliii. (1917) pp. 621-4. 



t Atti R. Accad. Lincei Roma, ser. 5, xxv. (1916) pp. 495-8. 



