INDUCED APOGAMY 



(Fig. 208^) and 36 pairs at meiosis (Figs. 209^, 210). In the little roots of apogamous 

 plants there are, however, only 36 chromosomes (Fig. 208c). 



The behaviour of these 36 chromosomes at meiosis is one of the principal points of 

 interest in this material, and though the actual number of mother cells available has 

 been very small indeed, being restricted to the two sori and one group of sporangia on a 

 prothallus above mentioned, enough has been seen for a few statements to be made. From 

 the two mother cells visible in Figs. 209 b, and 210b and c, at the stages of metaphase and 

 interkinesis, it is clear that meiosis is of the most irregular type possible. Chromosome 

 pairing (Figs. 209^, 210 b) is either completely absent or so shght that it cannot be de- 

 tected without a larger number of cells for inspection. Chromosome distribution at 



^P I 



•">. -H 







Wl 



n 



Fig. 209. Meiosis in sexual and apogamous Scolopendrium vulgare Sm., permanent acetocarmine. x 1000. 

 a. Sexually produced plant showing 36 pairs, b. Apogamously produced plant showing two 

 mother cells and tapetal nuclei. For explanation see text and Fig. 210^ and c. 



anaphase is apparently at random, and is most unequal, so that very dissimilar-sized 

 daughter nuclei are present in the succeeding resting stage (Figs. 209^, 210c). I have not 

 seen the second meiotic division, but the result of meiosis is total abortion of the spores. 



Such behaviour might have been expected and has indeed already been looked for un- 

 successfully in this and the two preceding chapters. The conclusion seems undoubtedly 

 to be that here at last we have a genuine haploid fern, comparable to the various well- 

 known cases of haploid sporophytes obtained in Flowering Plants but which, in the 

 Pteridophyta, had appeared to be curiously elusive. The failure of pairing among the 

 various chromosomes is almost certainly due to lack of homology between them, which 

 is to be expected in a genuine monoploid set. That « = 36 has, indeed, been shown to be 

 a fundamental monoploid condition in several related genera {Asplenium, Ceterach, Scolo- 

 pendrium) makes this conclusion the more probable, and therefore for once we may discard 

 all suspicion of harbouring a concealed hybrid or polyploid and accept the demonstra- 

 tion that apogamy provides that Scolopendrium vulgare is a simple diploid species without 

 any ambiguity. 



It would, however, be interesting to know still more about it. A repetition of these 

 observations on normal forms of the wild species might not be impossible and would be 

 of great value if it resulted in more abundant meiotic material. This would have more 



206 



