4 MASS. EXPERIMENT STATION BULLETIN 413 



inspection gives opportunit\- to detect mixtures before budvvood is desired for 

 propagation and since the relative freedom from insect and disease damage at 

 this tim.e tends to facilitate rapid inspection, the writers and their colleagues 

 have in recent jears examined fruit nursery stock for trueness-to-name during 

 the month of July so far as possible. 



Nursery trees often vary in appearance when growing in widely separated 

 localities. However, though the usefulness of particular characters may vary, 

 the identification of varieties in the nurser\- row is feasible no matter where 

 grown so long as good growth is being made. 



How Plum Varieties Differ 



There are many plant characters of importance in distinguishing one variety 

 from another. Sometimes the presence of a single character is sufficient for 

 positive identification; more often several to many characters are considered. 

 Those found most useful are briefly described here. In the accompanying illus- 

 trations (Figures 1-1 1), specimens have been chosen to emphasize some of the 

 more important distinguishing characteristics. 



The habit of growth usualh- refers to the direction and length of individual 

 shoots of two-year trees. It may var\- from spreading to upright, with most 

 varieties falling in the classification of upright-spreading. Tree height and stout- 

 ness of branches and shoots may refer to both one- and two-year trees. Some- 

 times the length of internode, space between buds along a shoot, is of some value. 

 The bark may be of value in both one-and two ->ear trees. Two-year trunk 

 bark varies from light brown as in Yellow Egg, through medium brown as in 

 Bavay, greenish brown as in Wickson, and gray brown as in Beaut\-, to dark 

 brown as in American Mirabelle. Bark color is a variable character, but in 

 general, varietal difTerences are worth noting. One-year bark is usually more 

 green, purple, and red and less brown than two-\ear bark, although the char- 

 acteristic color of the latter is approached near the base of a one-year tree. 



The color of young shoots is usually greenish at least near the growing tips. 

 Lower down, the older parts of shoots may take on some other color, usually a 

 red or purplish tinge. The amount of this coloration varies not only with shoot 

 age but also with tree vigor and other factors. However, the color of \oung 

 shoots is often a very valuable varietal characteristic. When shoot color is 

 mentioned in the descriptions, it usually refers to the color of these young shoots. 

 Older shoots gradually assume the features of one-year bark. 



The surface character of bark is often important (Figure 1). Elephant Heart 

 is glabrous or without pubescence or hairs; it is very smooth and even glossy. 

 Bradshaw appears glaucous due to a very fine pebbling of the bark. It is not 

 true glaucousness. Shropshire has true scarfskin which checks and can be scraped 

 oflF easily leaving the bark smooth; Beaut\- has a netted russet epidermis, while 

 on Burbank it is ridged. In Beaut\- and Burbank, it is not easily scraped off and 

 does not leave smooth bark below. The lenticels on both shoots and older bark 

 may differ in number, size, and color. Although they often do not vary suffi- 

 ciently to aid in identification, in some cases the>- are helpful. For example, the 

 number varies from ver>- few as on Blue Rex Damson to ver\- manj- as on Santa 

 Rosa. The.\- are usuaH>' flush, but Monitor and a few other varieties have raised 

 lenticels that feel rough to the touch. Lenticels may be inconspicuous as on 

 Elephant Heart or conspicuous as on Red June. Although usually russet in 

 color, they may be whitish as on French Damson. Lenticels are more useful 

 with Japanese than with European varieties. 



