SOME CHROMOSOME COUNTS IN THE EUROPEAN CISTACEAE 



By M. C. F. Proctor 

 Botany School, Cambridge* 



The Cistaceae are a small and rather homogeneous family, distributed chiefly in the 

 Mediterranean region. A few, including the four British species, extend into central and 

 northern Europe, and others occur in the west Asian steppes, the Arabian and north 

 African deserts, and the Atlantic islands. In addition a number of species, which will 

 not be considered further here, are confined to the New World. The Linnean genus 

 Cistus originally included all the European Cistaceae, but these are now invariably sub- 

 divided. Grosser (1903) in his monograph of the family recognises five genera, and I 

 follow most recent authors in adopting them throughout this paper. 



A number of chromosome counts of species of Cistaceae exist in the literature, but 

 taken as a whole they are unsatisfactory. Few have been based on wild material of known 

 origin, and some seem certainly to be wrong. The position in Cistus itself is clear. Many 

 counts have been made by several workers with the uniform result 2n = 18 in all the 

 species investigated (Chiarugi, 1925, 1937; Collins in Warburg, 1930; Bowden, 1940; 

 La Cour in Darlington & Janaki Ammal, 1945). The published records for Helianthemum 

 s.l. present a much more confused picture, which it is the attempt of the present paper 

 to clarify. 



Counts have been made of both mitotic and meiotic chromosomes. Mitosis was 

 examined in root tips obtained either from germinating seeds or from pot-grown plants. 

 The roots were cut off, pre-treated with 0-002 M 8-hydroxy-quinoline for 4-6 hours, and 

 then fixed in Carnoy's fluid. Maceration and staining were combined by heating the 

 roots in a little acetocarmine in a test-tube over a boiling water-bath for 5-10 minutes. 

 Iron was introduced either by standing a needle in the test-tube for a short time or by 

 adding a drop of an iron acetate solution. The root-tips were cut off on a slide, teased 

 in a drop of 45 per cent acetic acid, tapped out and squashed in the usual way. Acetic 

 orcein gave better results with pollen mother cell preparations for meiosis. A few anthers 

 were squashed in a small drop of the stain with a fine pointed scalpel, the anther debris 

 was removed and the preparation covered and squashed. Preparations were made per- 

 manent by inverting the slide in a dish of 50 per cent alcohol until the coverslip separated. 

 The slide and coverslip were dehydrated separately, and recombined in a drop of 

 ' Euparal.' 



The chromosomes were drawn using a camera lucida, at a magnification of about 

 X 1,800. A Leica camera with a microscope adaptor was used for the photographs. 



Almost all the plants used were of known wild origin, and documented herbarium 

 specimens of most have been deposited in the Cambridge University Herbarium. 



The results are listed in the following table. In general they differ from genus to 

 genus, but within a single genus show a considerable degree of regularity. Some confirm 

 existing counts, but in a number of cases published figures show discrepancies which 

 will be discussed in more detail below. 



*Now Nature Conservaancy, Bangor. 



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