THE CYTOLOGY OF BRITISH SPECIES OF EUPHRASIA 



By P. F. Yeo 



University Botanic Garden, Cambridge* 



The counting of the chromosomes of Euphrasia species was undertaken in connection 

 with an investigation of the breeding system and fertihty relationships of the British 

 species. 



Previous Work 



There has been Httle previous work on the cytology of European species of Euphrasia, 

 and as far as is known to the author, none of this has been on British material. 



Four species were counted by von Witsch (1932); they were as follows : E. minima 

 Jacq. subsp. minima (not British), n=22; E. rostkoviana Hayne subsp. rostkoviana, n — 11; 

 E. montana Jord., n=ll ; E. salishurgensis Funck, n=22. In addition A. & D. Love (1948) 

 report that Sorensen and Westergaard found n=22 in E. frigida PugsL, in Greenland. 

 Maude (1939) records 2n=44 for " E. confusa PugsL {minima auctt. angl.) von Witsch, 

 1932," but as shown above, it was E. minima Jacq. that von Witsch counted. Finally, 

 Tischler (1950) gives the entry " E. brevipila Burn, et Gremli (E. montana Fries) n = ll, 

 von Witsch (1932)." This must refer to von Witsch' s count of E. montana Jord. All 

 the names used by von Witsch are current names for well-known species and there 

 seems no reason to suppose that he cited his authorities wrongly. 



Method 



(1) Material 



The use of root tips was not attempted. Root tips would be very difficult to obtain 

 from wild plants owing to the slenderness of the roots, and their consequent fragility. They 

 could, however, have been obtained from young seedlings, but when this work was started 

 the few seedlings available were wanted for cultivation. Work was therefore confined 

 to the use of pollen mother cells. 



(2) Collecting 



Observations on cultivated plants showed that flowers at successive nodes open at 

 intervals of three or four days, or, in the case of E. pseudokerneri, five to seven days. Meiosis 

 thus occurs in any one spike with this frequency, and takes place roughly four or five 

 nodes above that of the flower open at the time. It should thus occur periodically from 

 about a fortnight before flowering starts until a fortnight before it ceases. Actually it 

 probably ceases earlier, because flowers at the last few nodes open at shorter intervals, 

 and there may be flowers open at two or three successive nodes simultaneously, so that 

 just before it stops flowering the plant becomes very floriferous. Meiosis seems to be 

 farther advanced when flowering is about to end, since it is found to have taken place 

 in smaller flower-buds than usual. For fixing, therefore, good solid shoot apices with 

 plenty of young bracts have to be chosen. These occur on the more luxuriant plants. If 

 the plants are growing under unfavourable conditions, flowers may be produced at only 

 three or four nodes, and then meiosis may be over when the first flower opens. As a 

 result of this, material of E. cambrica obtained in 1952 proved completely useless. 



* The work reported in this paper was carried out during the tenure of a Research Scholarship at the University College of 

 Leicester, 



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