314 INTRODUCTION TO CYTOLOGY 



fusion in the life cycle is that observed in the ascus, and that 

 this fusion is the real sexual act.] 



[(e) Fusion of two haploid sporocytes: In Aspidium falcatum (R. F. 

 Allen 1911) a haploid sporophyte arises by vegetative apogamy 

 from a haploid gametophyte. In the sporangium the 16 

 haploid sporocytes fuse in pairs, producing eight diploid cells 

 (Fig. 125, A). In these cells reduction occurs, 32 haploid 

 spores resulting.] 



2. Eu-apogamy: no kind of sexual act. 

 (a) The gametophyte is haploid: 



(a) The sporophyte is developed from the unfertilized haploid 

 oosphere : no such case of true parthenogenesis has yet been 

 observed. [Kusano (1915) has observed the division of 

 the haploid nucleus of an unfertilized egg in a few excep- 

 tional cases in the orchid, Gastrodia elata. Parthenogenetic 

 development proceeds no further. The unfertilized egg of 

 Fucus has been made to begin development by artificial 

 means (Overton 1913), but the cytological facts are not 

 known here. Motile gametes of certain other algae have 

 been observed to develop without conjugation, as in 

 Ectocarpus tomentosus (Kylin 1918).] 



(j8) The sporophyte is developed vegetatively from the gameto- 

 phyte and is haploid : observed in the prothallia of certain 

 ferns, Lastrcea pseudo-mas, var. cristata-apospora (Farmer 

 and Digby 1907), and Nephrodium molle (Yamanouchi 

 1908). [In the gametophytes of Nephrodium molle, which 

 has antheridia but no functional archegonia, Yamanouchi 

 found no nuclear migrations such as Farmer described 

 in Lastrcea (see Id) ; but there was haploid grafted tissue, 

 from which a haploid sporophyte developed. In Nephro- 

 dium hirtipes (Steil 1919) a haploid sporophyte arises by 

 vegetative apogamy from a haploid gametophyte. When 

 there are eight sporogenous cells in the sporangium there 

 is an incomplete nuclear and cell division (Fig. 125, B), 

 each nucleus coming to have the diploid number of chromo- 

 somes. These eight diploid cells function as sporocytes 

 and produce 32 haploid spores. Steil at first (1915) 

 adopted Allen's interpretation (le) for his material, but 

 later decided that the phenomenon observed was one of in- 

 complete division, and not one of fusion. In this case, 

 as in Aspidium falcatum, apogamy is offset not by apospory 

 but by an abnormal course of events in the sporangium. 

 In Aspidium falcatum the sporophyte arises as in the 

 examples mentioned in this paragraph, but because of 



