THE POLYPLOID SERIES IN OSMUNDA 



Table 5. Chromosome numbers of germinating spores derived from autotriploid 



Osmunda (3n = 66) 



Chromosome number 



No. of spores 



15 spores, 1942 



10 spores, 1943 



3 spores, 1944 



Total 28 spores ... 1121141572. 11 



Table 6. Chromosome numbers of germinating fresh spores of autotetraploid 



Osmunda (4^ = 88) 



Chromosome number 



while others reach adult stature but are misshapen and imperfect, and though they 

 may live for years are unable to complete their life cycle. This is, indeed, the fate 

 of the majority, and offspring can only be obtained at all if spores are sown on 

 a very large scale. 



As a result of repeated large-scale sowings and much patience, twenty-four descen- 

 dants of a triploid plant have been accumulated. They are very varied in appearance 

 as Fig. 28 will show; some died young and others seem unable to develop fertile 

 fronds although of an age to do so; a few are perfectly normal. The distribution 

 of chromosome numbers among them is highly significant. Had the average type 

 of spore reached sexual maturity it would be expected that the triploid chromosome 

 number would predominate in the progeny, although of course not the original triploid 

 constitution. This is, however, not the case. As summarized in Table 7, the majority of 

 such plants approximate to the diploid condition as regards chromosome number, 

 though the prevalence of structural abnormalities (Fig. 28) is sufficient evidence that 

 they are not all strict diploids of the normal kind. 



Table 7. Chromosome numbers of young sporophytes raised by sexual reproduction from spores 



derived from autotriploid Osmunda (3^ = 66) 



Chromosome number 



A 



No. of plants c. diploid c. triploid c. tetraploid 



24 21 2 1 



The degree of approximation to diploidy has only been exactly determined in 

 those plants which had become fertile up till 1944 when the observations had to be 

 discontinued. These amounted to six plants, of which two were exactly diploid, one 



41 



