40 MASS. EXPERIMENT STATION BULLETIN 413 



Variety Keys 



A variety key is an arbitrary classification of varieties based on a few selected 

 characteristics and arranged in such a way that a variety may be identified 

 rather quickly by following through the key. However, such a key is not in- 

 fallible since it is based on characteristics that exhibit natural variation, as for 

 example, color and size. Nevertheless, if used with discretion, a good key may 

 often be useful in variety identification. The following two keys include the 

 varieties considered in this bulletin. Since the varieties naturally group them- 

 selves into two categories, two keys are given instead of one single key. Nursery 

 trees of the European and Damson plums are, in general, easily distinguished 

 from the Japanese and Japanese- American hybrid varieties by the coarser leaf 

 texture of the former more U-folding in contrast to V-folding, more deeply 

 serrated margins, less acuminate leaf tips, fewer glands, fewer and less conspicuous 

 lenticels and scarfskin, and more purple color on shoots and bark. None of the 

 Japanese or hybrid plums have pubescent shoots, while many European varieties 

 are characteristically pubescent. 



These kevs are based on plant characters of healthy and vigorous one- and 

 two-year-old nursery trees as they appeared in late June and July. In general, 

 though the characters as described may be affected by a changed environment 

 due to location or season, varieties maintain their relative order for each character 

 so that a key may be useful over a wide range of growing conditions. Alderman 

 and Shoemaker (1) have made a key for 35 varieties commonly grown in the 

 Upper Mississippi Valley. However, except in a very few cases, the varieties 

 are not those discussed in this bulletin and consequently the identifying charac- 

 ters used in the respective keys are somewhat dissimilar. 



KEY TO EUROPEAN AND DAMSON VARIETIES 



A Shoots glabrous or nearly so 



B Growing tips prevailingly green 

 C Leaf surface semi-glossy 



D Leaf color medium green, leaf rigid, much twisted *9 Bradshaw 

 DD Leaf color daik green, lenticels fairly conspicuous 32 Lombard 

 CC Leaf surface mostly dull 



D Leaf color light yellowish green 56 Yellow Egg 



DD Leaf color medium green 



E Leaf rather small, round-oval, twisted 39 Pond 

 EE Leaf medium in size, long-oval to 



obovate 21 General Hand 



BB Growing tips usually reddish tinged, occasionally reddish 

 C Leaf surface semi-glossy to glossy 



D Leaf margin finely waved, rather coarse serra- 

 tions 25 Grand Duke 



DD Leaf margin medium to coarsely waved 



E Leaf large, flat to broad U-folded or saucer- 

 folded 

 F Serrations very fine, serrate; leaf very 



glossy 40 President 



FF Serrations medium in size, crenate. . . 6 Bavay 

 EE Leaf moderately small, medium U-folded . 43 Sannois 

 CC Leaf surface mostly dull 



D Leaf medium to narrow U-folded 



E Leaf rather light yellowish green, serrations 



rather fine 29 Imperial Epineuse 



EE Leaf medium yellowish green, serrations 



rather coarse 49 Stanley 



