370 University of California Puhlications in Agricultural Sciences [Vol. 



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ATTEMPTS AT SPECIES CROSSING 



The cases of recorded species hybrids in Trifolium are listed by 

 Karpechenko (1925) and Bleier (1925). In all cases one of the 

 parents Avas a species with a high chromosome number, T. lyannonicum 

 (130) or T. medium (80). Hitherto, however, no report has been 

 given of an P^ hybrid which has been cytologieally investigated. 

 Crosses were attempted between nine species in eighteen different 

 combinations. The material was the same as that used for cytological 

 investigations. The methods used were mainly two : 



1. The heads were enclosed in paper bags before any floAver had 

 opened. 'Emasculation was performed when the head was about half 

 developed. The flowers which were either too old or two young were 

 cut away and in the rest of the flowers the anthers were removed with 

 a forceps. This operation is fairlj^ easy in the species Avith large 

 flowers, but difficult in the small-flowered ones. The flowers were 

 mostly pollinated immediately after emasculation, in some cases the 

 next day. All the instruments used were washed in alcohol frequently 

 during the work and only very few cases of selfing occurred. 



2. Using plants of self-sterile species as mother plants, the pollen 

 from other species was applied without emasculation to the stigma in 

 flowers Avhich had been bagged before opening. 



Cross Number of flowers crossed 



1. T. pratense X T. incarnatum 950 



2. T. pratense x T. repens 327 



3. T. pratense x T. hyhridum 284 



4. T. pratense x T. fucatum 61 



5. T. pratense x T. virescens 154 



6. T. pratense x T. ohtusiflorum 32 



7. r. repens x T. hyhridum 129 



8. T. repens x T. incarnatum 20 



9. T. incarnatum x T. alexandrinum 186 



10. T. incartmtuin x T. reflexum 26 



11. T. incarnatum x T. ohtusiflorum 290 



12. T. incarnatum x T. virescens 92 



13. T. virescens x T. fucatum 33 



14. T. virescens x T. ohtusiflorum 6 



15. T. virescens x T. reflexum — 



16. T. ohtusiflorum x T. fucatum 6 



17. T. ohtusiflorum x T. reflexum 15 



18. T. reflexum x T. ciliolatum 11 



