INDUCED APOGAMY 



of their perfect morphology. They may all therefore be suspected of being genetically 

 unbalanced. 



Meiosis has been studied as far as is possible in sections in both types of plant, and the 

 comparison, in view of their previous history and consequent pecuHar relationship, is 

 one of the principal points of interest about them. Fig. 206 a shows the first meiotic meta- 

 phase in a normal sexually produced plant, and Fig. 207 is of diplotene or very early 

 diakinesis in the only squash preparation which I had the opportunity of making. 

 Neither is suitable for detailed counting, although both show clearly the perfect regular- 

 ity of the division without either unpaired chromosomes or multivalent groups. Fig. 



Fig. 205. Sporangia and spores oi Doodia caudata (Cav.) R.Br, x 100. a. An apogamously 

 produced plant, b. A sexually produced sister plant. 



206 b, on the other hand, shows meiosis in one of the apogamously produced plants. The 

 much smaller size of the cells, no less than the irregularity of the metaphase plates, strikes 

 the eye at once. This is as expected. It might, however, also have been expected that if 

 this plant is indeed a haploid only unpaired chromosomes would be found, yet this is not 

 the case. Univalents are certainly never absent, but they represent only a small propor- 

 tion of the whole. Numerous pairs, visible on the equator even at the relatively low 

 magnification of the photograph, are present also, and it is even possible that there are 

 some multivalents. Pairing of this kind recalls somewhat the behaviour of the sixteen- 

 celled sporangia of Pteris cretica, and the most probable interpretation would appear to 

 be, as in that species, that the chromosome number of the apogamously produced plants 

 of Doodia, though gametophytic, is not haploid. We seem to be deahng with diploid 

 derivatives from a tetraploid stock which was itself allopolyploid. Or in other words, 

 with a strain of Doodia which, beneath its regular pairing achieved by a chromosome 

 doubling which the conditions of the experiment have reversed, contains two different sets 

 of chromosomes between which considerable though not complete homology exists. 

 Two gametic sets of this type are likely to be derived from distinct though related 

 species, and we reach the somewhat unexpected conclusion that the D. caudata used by 

 us and in cultivation at Kew is another case of a concealed species hybrid. 



202 



