•_'() SYSTFMATK 1'<)M(HJK;Y 



of it may reiiKiin. The ^'rct'ii layer may he in evidence only in 

 the current season's <rrowth. In some prapes even the hast layer 

 may die and h»osen ^vhe^e it han^^s in shreds alter the first or 

 seeond year. 



Nearly all of the many si)eeies of Prunns can he roeoprnized 

 from their hark. Color, thickness, and smoothness are all im- 

 portant. In the drupe-fruits the color of the inner as well as 

 the outer hark must he noted as there are in some species de- 

 l)osits of coloring: matter. Bark is usually liofhter in color in 

 warm than in cold climates. On young: healthy vigorous plants, 

 it is smoother and hrighter than on old decrepit or diseased 

 trees. The hark of all perennial plants is shed in scales, strips, 

 or flakes as ag:e prog:resses from the outside. This process is 

 called exfoliation, and the manner of it is often a fine mark of 

 distinction, especiall}' in the drupe-fruits. 



In the apple, oblong scales of various sizes detach themselves 

 at ends, at sides, clinging at the middle, and finally fall to the 

 ground. In old pear trees the bark is checked in squares; in 

 the cherry thin strips peel from around the tree ; in the peach 

 the manner of exfoliation is more varied than in most other 

 fruit-trees. 



32. Lenticels. — lender the strain of growth the epidermis 

 of twigs, hranehlets, and branches bursts at the stomafa, the 

 breathing pores of the epidermis, exposing a corky or powdery 

 mass of cells through lens-like rifts from the shape of which is 

 given the name lenticel. The corky cells exposed are usually 

 brownish or Avhitish. These organs may serve for the admission 

 of air and for the diffusion of gases inward and outward. 

 Lenticels var>^ greatly in number, position, size, and shape in 

 different genera, species, and varieties and may be very helpful 

 in identifying winter wood of any of these groups. On the 

 apple, pear, plum, peach, cherry, and related fruits they must 

 always be taken into account in describing the wood. 



33. Color and bloom of bark. — In young trees the color of the 

 bark is a most valuable diagnostic character. Many if not most 

 pome-fruits can be told in the nursery by the color of the bark, 

 but color does not help much in identifying the drupes. Especial 

 attention must be paid to the color and the bloom of stems in 

 the brambles. The stems of cultivated brambles may be tints 



