182 



VARIATION IN ARUM MACULATUM 



whose help is gratefully acknowledged. The results are shown on the map (Fig. 1) which 

 shows clearly that the unspotted form becomes more frequent as one goes further north; 

 there is clear evidence of a cline. The existence of this cline helps to confirm the northern 

 limit of the species. It would be reasonable to regard most of the isolated clumps of 

 spotted plants in northern Scotland (e.g. Aberdeen, Angus) as introduced, a view held 

 by most local observers. Sowter (1949) draws the northern liniit of the species between 

 the River Forth and Argyll, and this is supported by the evidence from the cline. Thus 

 there are twelve spotted to four unspotted records north of Sowter' s line, but four spotted 

 to fourteen immediately south of the line. If the above explanation is correct, it does 

 not explain why the spotted plant was introduced rather than the unspotted. Possibly, 

 it was considered the more ornamental, or perhaps it was more common at the time of 

 introduction. Moreover the cause of the cline itself remains unexplained. 



On the continent. Hock (1934) records a different result, considering the spotted 

 form commoner in North Germany than in the South. All the native plants of Denmark 

 are unspotted, but these belong to a separate chromosome race (2n = 28). 



In addition to the change in the degree of spotting the size of the plant in this country 

 decreases as one goes further north. The luxuriant growth of the southern plants, which 

 sometimes reach 30 cm., gradually diminishes, 15-20 cm. being the normal height of the 

 Scottish plants. 



The leaves of A. maculatum contain cyanophoric glucosides. Several hundred tests 

 (Prime 1951) indicated differences in the glucoside content, but these did not appear to 

 be correlated with any other variation. 



The stomatal index is not so constant as in other species, and there is no significant 

 difference between plants from different localities, or plants with differing chromosome 

 number. Stomatal index determinations varied from 7-0 to 11-5, the average being 9-28. 



2. Floral variation 



Miller Christy (1914) drew attention to the rolling of the spathe; if it is rolled anti- 

 clock-wise from above he described it as sinistral, if conversely as dextral. In over 1,200 



Table 3 



The numbers of sinistral and dextral spathes 



Approximate 

 level of 

 statistical 



Locality 



Sinistral 



Dextral 



significance 



Observer 



Date 



Essex 



645 



583 



10% 



Miller Christy 



1914 



Hereford 



278 



220 



10% 



Armitage 



1921 



Croydon, Surrey 



106 



91 





Prime 



1946 



Croydon, Surrey 



537 



463 



3% 



Prime 



1947 



Croydon, Surrey 



560 



440 



•1% 



Prime 



1948 



Northumberland 



36 



18 





Temperley 



1949 



Aberdeen 



11 



8 





Kerr 



1949 



Beckenham, Kent 



55 



45 





Sherwood 



1949 



Culford. Suffolk 



10 



7 





Thompson 



1950 



Whitby, Yorks. 



11 



6 





Little 



1950 



Bryanston, Dorset 



13 



12 





Hawkins 



1950 



Mildenhall, Suffolk 



349 



314 



20% 



Southwell 



1950 



Stroud, Gloucester 



24 



35 





Hughes 



1950 



Alton, Hants. 



179 



140 



13% 



Langridge 



1950 



Swindon, Wilts. 



190 



157 



10% 



Timperley 



1950 



Bristol, Glos. 



22 



17 





Timpeiley 



1950 



Total 



3026 



2556 



•1% 







