ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 323 



Antithetic versus Homologous Alternation.* — D. H. Campbell 

 discusses the main arguments put forward in favour of the two rival 

 theories as to the origin of the Bryophyta and Pteridophyta, Accord- 

 ing to the Antithetic theory, the ferns originated from forms very 

 similar to the simpler existing liverworts, the leafy sporophyte being 

 an elaboration of the non-sexual sporophyte. The Homologous theory 

 maintains that the Bryophytes and Pteridophytes arose quite indepen- 

 dently of one another from Algal ancestors — a hypothesis first suggested 

 by the alga-like protonema of the mosses, and the somewhat similar 

 prothallia of certain ferns, especially Trichomanes. These filamentous 

 structures the author, a supporter of the Antithetic theory, regards as 

 merely secondary developments. He insists upon the obvious resem- 

 blances in the gametophyte of ferns and hepatics, especially the structure 

 and development of the archegonium, and the early stages of the sporo- 

 phyte and the extraordinarily uniform method of spore-production. 

 The sporophyte of Anthoceros in many ways offers the nearest approach 

 to the Pteridophytes, as the author shows. Apogamy is the strongest 

 argument in favour of homologous alternation, but, as it has only been 

 observed in the leptosporangiate ferns (i.e. the most recently evolved and 

 most specialised members of their class), and only in their cultivated 

 forms, apogamy appears to be a pathological phenomenon and not a 

 primitive function. Hence it is difficult to accept the homologous 

 theory that the sporophyte probably arose from the gametophyte as a 

 vegetative outgrowth. The author proceeds to reject this view for other 

 reasons. He gives reasons also for rejecting the view that the sporo- 

 phyte arose asexually from the gametophyte in response to a call for 

 increased chlorophyll activity. Purely vegetative shoots are of course 

 so produced ; but that these gave rise to the leafy sporophyte requires 

 evidence which is not forthcoming. Apospory and apogamy may be 

 compared to adventitious budding. The real explanation of the pecu- 

 liarities of the leafy sporophyte must be sought in the conditions of 

 water-supply. The bryophytes have never succeeded in emancipating 

 themselves from the aquatic habit. Their rhizoids are inadequate to 

 supply a plant-body of large size. The sporophyte, aerial in habit, by 

 means of its foot draws its water from the gametophyte ; and it was not 

 till a root of unlimited growth was evolved, that the sporophyte was 

 enabled to lead an independent existence and attain large dimensions. 



Californian Ferns.t — S. B. Parish gives an account of the pterido- 

 phyta of California, a State which, stretching 600 miles from north to 

 south, presents great diversity of climatic conditions in latitude, altitude, 

 temperature and rainfall. The latter varies from 60 inches annually in 

 the north to 5 inches or less in the southern deserts. Yet the flora 

 amounts to no more than 76 species. There is a lack of the moist 

 equable warmth which the ferns require for their best development. 

 In the north there is an abundance of a few species, mainly bracken ; 

 in the arid south the xerophytic genera — Pellim, Notholana and Chei- 

 lanthes — exhibit the greatest development. There is a mingling of 

 ferns of a northern and southern type, and it is the latter which are the 



* Amer. Naturalist, xxxvii. (1903), pp. 153-69. 

 t Fern Bulletin, xii. (1904) pp. 1-15. 



