REGIONAL VARIATION OF ALNUS GLUTINOSA 



31 



Cytology 



Chromosome counts, in seedling root tips, of " macrocarpa," " microcarpa " and 

 " typica " material from Chippenham and the West of Scotland all gave 2n = 28, the 

 diploid number. Larsen has reported the occurrence of tetraploid alders in Denmark 

 (Ording 1939), and Johnsson (1950) has described colchicine-induced chimaeras, with 

 diploid and tetraploid layers, as being stunted in growth, with large, irregularly lobate, 

 deeply toothed leaves which are often asymmetric, while wholly triploid plants had more 

 robust growth than diploids and strikingly large leaves. 



I Race Differentiation 



There are some references in the literature to the occurrence of races of different 

 provenance in Alnus glutinosa and to growth disturbances following the cultivation of 

 certain races in alien territory. 



Larsen (Ording, 1939) cites the losses suffered by Danish forestry through importation 

 of a type of alder, of more southern European origin, apparently not suited to the northern 

 climate. At Frijsenborg the local race of A. glutinosa develops much better than offspring 

 of even extremely fine trees at Meilgaard where the mother trees were even supposed to 

 be of the Frijsenborg race. 



Rubner (1934) refers to the poor growth of southern stock at Memel, Germany. 

 The plants grew very quickly and produced fruit prematurely. They were attacked by 

 the fungus Valsa oxystoma and died at the early age of 12-20 years. 



In the present work the only indication of this phenomenon, apart from the morpho- 

 logical differences described above, has been given by the different photoperiodic responses 

 obtained from populations from different latitudes. 



In 1950, seedlings, which had been raised in the greenhouse and hardened off in 

 the cold frame, were transferred to side-shaded plots at the Cambridge Botanic Garden 

 on April 27th. In the transfers some groups were subjected to greater temperature 

 changes than others, with the result that the different growth rates and final sizes attained 

 could not be attributed to racial differentiation. 



Difference in the time of leaf fall in November 1950 was, however, independent 

 of the initial differences in treatment. On October 31st the leaves of the Arran seedlings 

 had begun to brown while those of the Chippenham and North Wales plants were still 

 green. A background of fallen chestnut leaves made a useful, though primitive, colour 

 comparator, and on November 7th the Scottish seedlings were not visible against the 

 carpet while the remainder were. The colour difference was hardly visible after mid- 

 November, but the Scottish seedlings had by then shed more of their leaves. 



The difference in time of loss of leaf function was estimated at 2-3 weeks for four 

 degrees of latitude. About 75 seedlings were under observation. 



A smaller number of Arran and Chippenham seedlings were also grown together 

 in a plot near Glasgow where the different responses were even more marked than at 

 Cambridge, the native seedlings browning and losing their leaves about three weeks 

 before the others. 



In 1951 seedlings from West Inverness, Arran, Lancashire, North Wales and East 

 Anglia were grown in pots out of doors for one season. Significant differences in growth 

 rates could not be detected but differences in time of leaf fall were again apparent, the 

 leaves browning in the above order. 



The 1950 plants, now 1-3 ft. high, again showed three weeks' difference in time of 

 leaf fall between the Arran and southern groups. In the spring of 1952 the saplings of 

 southern origin were markedly earlier in flushing. 



Wareing (1948) summarises present knowledge of photoperiodic phenomena in 



