INTRODUCTION TO THE METHOD 

 however, sufficiently high to be indicative of aMtopolyploidy in the cytological sense, 

 by which is meant the duphcation of identical, i.e. 'homologous', sets of chromo- 

 somes throughout the series, ahhough the existence of slight genetical differences 

 between the sets is not thereby excluded. 





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40 



d - e f 



Fig. 2. Polyploidy in Biscutella laevigata L. a-c from Manton (1935a); 6?-/ from Manton (1937). 

 a. A diploid root of subsp. alsatica showing 18 chromosomes, from a section stained in gentian 

 violet. X 2000. b. A triploid root of a hybrid between subsp. alsatica and subsp. longifolia showing 

 27 chromosomes, from a section stained in haematoxylin. x 2000. c. A tetraploid root of subsp. 

 longifolia showing 36 chromosomes, from a section stained in gentian violet, x 2000. d. Chromo- 

 some pairing in the diploid showing 9 pairs, from a permanent acetocarmine preparation, x 1500. 

 e. Chromosome pairing in the triploid showing trivalents, pairs and univalents, permanent aceto- 

 carmine. X 1500. /. Chromosome pairing in the tetraploid showing quadrivalents and pairs, 

 permanent acetocarmine. x 1000. 



From the evolutionary point of view these facts show that the natural populations of 

 diploid and tetraploid B. laevigata in different parts of Europe are closely related 

 phyletically and that the diploids are the older type. The first of these conclusions 

 could have been deduced by the normal procedure of comparative morphology but the 

 second could not, and in this particular case the association of newer and older forms 

 with glaciated and unglaciated areas of central Europe respectively made it possible to 

 suggest some rough approximations regarding their relative ages and the paths of 



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