34 SYSTEM A'lIC I'oMtUJK.y 



vernation is said to he condiiplicdte. The leaves of all peaches 

 and clieri-ies ai'e conduiilicate in the hud. When the leaves are 

 folded like llie i)laits of a fan. tlH> venial ion is phiihd or plu'dtc. 

 The currant furnishes a ^ood example of ])laited vei'nation. 

 When the hlade is rolled parallel with the axis, vernation is 

 convolute {V\^. 23). The leaves of some i)lums ai-e eonduplicate 

 in the hud and of others convolute, so that manner of vernation 

 hecomes a fine mark of distinction in separating species. 



55. The petiole ilmf-sfalk) is a firm stalk-like support for the 

 green hlade, which often turns and twists, raises and lowers 

 on the petiole to positions where it can be illuminated best. 

 Petioles are more or less cylindrical and are usually chan- 

 neled or grooved on the upper side, these markings being dis- 

 tinctive in ditt'erent species. Perhaps the character of petioles 

 that serves best in classifying is length, which varies greatly and 

 is commonly constant in the species. Color and whether 

 pubescent or glabrous are marks of distinction that often serve 

 Avell. The petiole may be used to good advantage to determine 

 species and varieties of Prunus. Thus, in consequence of the 

 great length and slenderness of the petioles of sweet cherries, 

 the leaves droop, while because of the short stout petioles of sour 

 cherries, the leaves are erect, these differences in petiole giving 

 the two species distinctive aspects. The color of the petiole of 

 stone-fruits is usually correlated with that of the fruit. 



The petiole offers several important characters in currants. 

 The length distinguishes several varieties, that of Victoria being 

 remarkably long. The color and amount of pubescence are also 

 distinctive. In some currants the petiole is markedly channeled. 

 The angle at which the petiole holds the leaf-blade is a mark 

 in currants. Thus, the leaf-blade of Prince Albert is held stiffly 

 upright ; that of Victoria horizontally and lax ; while in Fay 

 the leaves point downward. 



The petiole of the strawberry leaf is of importance to the 

 systematist and to the grower. Length, color, and pubescence 

 are significant, but the way in wiiich the leaf-blade is held is 

 of prime importance. The leaves of some varieties are erect and 

 those of others prostrate ; erect leaves are more desirable, as 

 they are not so likely to be infected by fungi, and the flowers are 

 better protected from frost. 



