APOGAMY AND APOSPORY 59 



it has been shown by Farmer and Miss Digby that there is apogamy 

 as well as apospory. The cytological investigation shows that in those 

 cases where sporophytes were borne on the apogamous prothalli there is 

 not any migration of nuclei from one prothallial cell to another, such 

 as has been described for some cases of apogamy ; nor is there doubling 

 of the chromosomes in any other way. In fact, the chromosome-number 

 is the same for the sporophyte as for the prothallus which bears it. 

 Investigation of the aposporous transition from the leaf to the prothallus 

 showed also that no change of number marks the passage from sporo- 

 phyte to gametophyte. There is here a case of cytological uniformity 

 throughout the whole cycle, with chromosome-number about 90. This is 

 approximately the number found in the diploid stage of a typical Athyriitm 

 fiUx-foeinina. The condition of the variety is as though reduction had 

 been omitted from the cycle : as a consequence the prothallus being 

 itself diploid, fertilisation would be unnecessary to produce a new 

 sporophyte : accordingly apogamous budding will suffice, and that is what 

 actually occurs. 



A near parallel to this has been worked out with similar exactitude by 

 Strasburger in Marsilia Drummondii, A.Br. 1 The typical chromosome- 

 numbers are 16 and 32 respectively for gametophyte and sporophyte, 

 and normal plants show the usual succession of events. But on ger 

 mination of the megaspores -borne by certain plants, the gametophyte 

 was found to have the diploid character, and this was seen even 

 in the division to form the ventral-canal-cell : thus the ovum itself is 

 diploid. In such archegonia the neck does not open, so that fertilisation 

 by spermatozoids is impossible : the unfertilised diploid egg develops 

 apogamously into an embryo, which is naturally diploid also. An 

 examination of the sporangia showed further that while in typical Marsilias 

 the reduction to 16 chromosomes takes place as usual in the spore- 

 mother-cells, in M. Drummondii the megasporangia show two types of 

 spore-mother-cells : the one type is normal in number, and shows 

 reduction : the other type is produced in smaller numbers in the sporangia, 

 for instance only four in place of the usual 16 : these on division 

 have diploid nuclei, and the interesting fact is that their diploid state 

 does not divert them from the usual characters of form and structure. 

 Since the apogamous plants produce both diploid and haploid spore- 

 mother-cells, it is accordingly not surprising that both apogamous and 

 sexual plants should be produced from their sporocarps : and it is apparent 

 that among the representatives of the species there will be individual 

 cycles completed without any change of chromosome-number : certain 

 cycles will accordingly be diploid throughout. In this they correspond to 

 what is seen in Athyrium filix-foemina, var. clarissima, Jones, though 

 they differ in the detail that the diploid ovum here forms the embryo, 

 while in the Athyrium the embryo arises from the prothallus by apogamous 



1907. p. 123, etc. 



