692 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



second station in the Schwarzwald. Thirdly, he describes forking of the 

 frond of Blechnum spicant and Asplenium fiUx-femina in the same 

 region. 



Apogamy in Marsilia.* — E. Strasburger has investigated the ques- 

 tion of the production of embryos in Marsilia without fertihsation. 

 Some of the sporocarps which he germinated had been in herbaria for 

 more than thirty years. In some species, as M. Drummondi, the mega- 

 spores produce prothallia and embryos almost as abundantly in the 

 absence of microspores as in their presence. Embryos often develop 

 from unfertilised eggs, and their nuclei have 32 chromosomes, the 2 x 

 or sporophyte number. Some megaspores have nuclei with 2 x chromo- 

 somes, reduction of the chromosomes having failed to take place ; and 

 the same phase is maintained throughout the life-history, the prothallia, 

 eggs, and embryos all having nuclei with 2 x chromosomes. But in the 

 same species reduction also occurs, so that prothallia and eggs have nuclei 

 with the X or gametophyte number. In forms which produce apogamous 

 embryos, microsporogenesis is usually abnormal, spores oi '1 x phase 

 being produced ; but sometimes normal reduction of chromosomes takes 

 place. The nuclei of the x and 2 x prothallia and eggs are distinguish- 

 able by size, the 2 x sort being larger. Strasburger regards the 2 x egg 

 as purely vegetative, and therefore employs the word apogamy and not 

 parthenogenesis. But he would use the latter term in case an egg with x 

 chromosomes were to develop an embryo without fertilisation. He also 

 describes the development of the spore walls. 



Apogamy in Nephrodium.t — S. Yamanouchi gives a preHminary 

 account of his cytological studies on apogamy in Nephrodium molle Desv. 

 He treats his subject under the headings : Mitoses in the sporophyte ; 

 spermatogenesis ; oogenesis and fertihsation ; apogamy ; and states his 

 conclusions as follows. (1) The nuclei of the prothallia contain 64 or 

 66 chromosomes, the reduced, gametophytic, or x number. The nuclei 

 of the gametes contain the same number. The fusion nucleus in the 

 fertihsed egg presents 128 or 132 chromosomes, the unreduced, sporo- 

 phytic, or '2x number, which keeps unchanged until it is reduced during 

 sporogenesis. Consequently it follows in the normal life-history of 

 Nephrodium that the gametophyte contains the x number of chromo- 

 somes and the sporophyte the ix number, and that sporogenesis and 

 fertilisation are the periods which mark the initiation of the two distinct 

 generations. (2) The nucleus of a prothallial cell with the x number 

 of chromosomes (64 or 66) sometimes becomes directly the nucleus of a 

 sporophyte, apogamously produced ; so that the x number of chromo- 

 somes continues through the whole Ufe-history in the apogamous sporo- 

 phyte. This fact does not seem to affect the fundamental idea that the 

 alternation of generations is marked by the difference in the number of 

 chromosomes in the normal life-history, but is simply an abnormal case 

 of secondary importance. Still it must be admitted that in the case of 

 apogamy at least the number of chromosomes is not the only factor 

 which determines the character of the sporophyte and gametophyte. 



* Flora, xcvii. (1907) pp. 123-91 (6 pis.). See also Bot. Gazette, xliv, (1907) 

 pp. 70-1. t Bot. Gazette, xliv. (1907) pp. 142-6. 



