THE POLYPLOID SERIES IN OSMUNDA 



Since 1932 apospory of similar type has occurred spontaneously on several occasions 

 in young tetraploid sporophytes. The resulting prothalli are also tetraploid, but, 

 unlike the diploids, they appear to be sterile, for they are now over 10 years old and 

 are still barren in spite of liberal watering. 



The triploid sporophytes and gametophytes, which complete the series, have required 

 somewhat more careful preparation. The first triploid sporophytes were already 

 fully grown and fertile when their chromosomes were first examined in 1932. They 

 occurred intermixed with the tetraploids which had been grown on from the first 

 experiments, and two were found among seven plants. Their origin was at that time 



Fig. 12. 



Fig. 13- 



Fig. 12. The origin of the polyploid prothalli. Two 'leaves' from a young plant of Osmiinda regalis L., 

 the one on the left showing the normal juvenile lamina, but the one on the right abnormal in shape 

 and ending in a heart-shaped prothallus. From a photograph kindly supplied by Prof. W. H. Lang, 

 after Lang (1924). Twice natural size. 



Fig. 13. The origin of the polyploid sporophytes. Haploid and diploid prothalli fertilized on the same 

 day and grown on together. The normal (diploid) young plants on the right have grown much 

 faster than the tetraploid young plants on the left which therefore appear much smaller. Several 

 unfertilized prothalU can be seen creeping over the soil in the left half of the pot. Half natural size. 



uncertain but has since been traced to contamination of the original diploid prothalhal 

 cultures with some normal prothalh from self-sown spores. Triploids have been 

 synthesized on several occasions since by inseminating diploid archegonia with 

 haploid spermatozoids, and they are not produced if the diploid prothallial cuhures 

 are kept pure. Though more troublesome to produce in large numbers than are the 

 tetraploids, such young triploid plants can be made to become aposporous in the 

 same way as the others. The method adopted by Mr Ashby, who has been entirely 

 responsible for this part of the work, was to mutilate a young triploid plant by repeatedly 

 removing its roots until the depauperate condition associated with leaf abnormahties 

 was achieved. One aposporous prothallus was developed which has since been grown 



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