REGIONAL VARIATION OF ALNUS GLUTINOSA 



29 



presented in histogram form. Catkin and length breadth have been multiplied together 

 to give simple numbers which express size more adequately than either linear dimension. 

 It can be seen from histogram 2* 1-7 that catkin size forms a unimodal curve slightly 

 skewed towards the smaller sizes. 



Fig, 2. Size distribution of alder catkins in each district studied. Catkin length X catkin breadth is expressed 

 as " mm. units " on the abscissa, and the ordinate gives number of catkins measured. 



1. EastAnglia 2. North Wales 3. Mid Scotland 



4. N.E. Scotland 5. Deeside 6. Glen Nevis 



7. Sutherland (see Fig. 3) 



Since the method of sampling has resulted in the variation studied being non- 

 homogeneous (compounded of that " within a tree " and " between trees ") only differences 

 in means of at least three times the standard error have been regarded as significant (i.e. a 

 level of significance of 0-27 per cent). 



It has been found that each population is not significantly different from its near 

 neighbours but that significance increases with distance. Thus Santon Downham, 

 Chippenham Fen and Ranworth Broad populations are not significantly different nor 

 are those of Sutherland, but any one of the first group is significantly different from 

 any of the second, 



