SOME CHROMOSOME COUNTS IN THE EUROPEAN CISTACEAE 157 



(a) Halimium 



The three species counted all have a diploid number of 18, which agrees with the 

 counts of n = 9 in H. halimifolium and 2n = 18 in H. atriplicifolium (Lam.) Spach given 

 by Chiarugi (1925, 1937). 



(b) Tuheraria 



This genus provided two rather surprising diploid counts of 14 and 36, both, I believe, 

 not previously recorded. Of the published figures for T. guttata, Bowden's 2n = 20 

 (1940) is almost certainly an error due to wrongly named material. Chiarugi (1925) 

 found n = 24, and this count deserves more consideration. The occurrence of as low 

 a number as 2n = 14 in T. vulgaris suggests that T. guttata with 2n = 36 must have 

 arisen as a polyploid. It seems most likely that it is a hexaploid on a basic number of 6, 

 so that, whatever its exact mode of origin, plants with other multiples of this number, 

 especially 12 and 24, should be sought. The four counts published here are from only 

 a small part of the area of the T. guttata complex, and it is quite likely that other numbers 

 may occur in other parts of the range. Cytological investigation both of other T. guttata 

 forms, and of the remaining perennial species, T. glohulariifolia (Lam.) Willk., would be 

 well worth while. 



(c) Helianthemum 



Two differing chromosome numbers occur in this genus as in the last. In the species 

 investigated, those of the subgenus Helianthemum have 2n = 20, while those of Plectolobum 

 have 2n = 22. However the genus is a large one, and more counts would be needed to 

 establish that this represents the full variation, especially as the material studied leaves 

 several sections unrepresented. Most of the more recent published work is consistent 

 with these results, but Bowden (1940) obtained diploid counts of 32 in H. apenninum 

 and H. chamaecistus, and Mattick (in Tischler, 1950) 32 in H. chamaecistus which agree 

 with the earlier determinations of Chiarugi (1925). It is difficult to see how a mistake 

 can have occurred, though the triploid garden forms of Helianthemum reported by Snoad 

 (1954) with a somatic chromosome number of 30 suggest one possibility. On the 

 evidence now presented, appears to be cytologically uniform over a wide area with 2n = 20 

 (Fig. 2). The forms investigated embrace the greater part of its morphological variation, 

 and it semes unlikely that there could actually exist a chromosome race with as unrelated 

 a number as 2n = 32. Apart from my counts, 2n = 20 is quoted by A. & D. Love (1948) 

 from Scandinavian material, and it has been determined by K. Larsen (Dr. T. W. Bocher 

 in litt.) from the following localities : dry field in Pinus wood between Angouleme and 

 Bordeaux, France; dry slope in the valley at Luchon, Pyrenees, France; dry alvar on 

 Gotland, Sweden. Bowden's ' H. alpestre ' with 2n = 20 was probably a small form 

 of H. chamaecistus. A plant of H. alpestre from Interlaken, Switzerland, agreed quite 

 clearly with H. canum and H. oelandicum in its haploid number of 11, as would be expected 

 from its taxonomic relationships. The counts given here for H. canum from Teesdale and 

 Westmorland confirm those published by Tutin (1953) from the same localities. 



(d) Fumana 



Few counts are available for Fumana species. Such as there are suggest a uniform 

 diploid number of 32, the number obtained by me for F. laevipes, but most are old and 

 need confirmation. 



A number of errors have been indicated in the published chromosome numbers of 

 the Cistaceae, and some comment on accuracy in chromosome counts seems called for. 

 Errors may arise in two ways : either through poor technique, or through wrongly named 



