CROWN-ROT OF FRUIT TREES: HISTOLOGICAL STUDIES 511 
Fig. 34. Cross-section of a large dead streak of phloem surrounded by modified 
irregular parenchyma. 
Fig. 35. Similar view of a living streak in the phloem surrounded by layers 
of dead, collapsed cells. 
Plate XXV 
Initial injuries followed by another type of regeneration. All from maple 
except Fig. 41, which is from pear. 
Fig. 36. Series of magnified views of a portion of Fig. 37, from old bark {oh) 
to old wood {ow): a, old bark {oh) run through by rifts, new bark {nh 1) with inclu- 
sions of dead masses, and new cambium {nc i) just outside some new wood shown at 
the outer edge of outer new wood {nw i) in Fig. 37; h, from the inner edge of the 
outer new wood {nw 1) of Fig. 37, showing the new cambium {nc 2) and some very 
irregular new bark {nh 2); d, from the outer edge of the inner sheath of new wood 
{nw 2) of Fig. 37, nh 2 and nh 3 together constituting the compressed new bark 
between nw 1 and nw 2 of Fig. 37. e, higher power view of line oc of Fig. 37, showing 
some detail. 
Fig. 37. Cross-section of maple tree {Acer plafanoides) with a season's growth 
added after the occurrence of the initial injury, that had been similar to that shown 
in Fig. 3, and somewhat like that shown in Fig. 38. Three cambial layers have 
developed in place of one. The tangential cleft left some living phloem adhering to 
the old wood like that shown in Fig. 3. Substitute cambium arose in the strip of 
inner phloem adhering to the wood, giving rise to c 3 of Fig. 37; then along the 
inner surface of the loosened outer bark another cambium developed which gave 
rise to new wood in its middle and was thus divided into two cambial sheaths {c 1 
and c 2), each producing wood and bark. Activity of three cambial layers, as 
detailed in Fig. 36, gives rise to unsightly enlargements like that shown in Fig. 40. 
Fig. 38. Section of box-elder tree {Acer Negundo) with portion of its bark 
separated from the wood, though still living. Beginning of callus formation is 
shown along the edges of the loose bark (May 28). 
Fig. 39. Higher power view of a portion shown in Fig. 26e; considerable regen- 
eration-growth of wood outside the zone of iiiitial injury, which subsequently died 
and became discolored. 
Fig. 40. Trunk of a street tree {Acer platanoides) unduly enlarged near the 
upper part of the trunk owing to the activity of three cambial zones developed after 
the occurrence of some injuries initially much like those shown in Fig. 3. 
Fig. 41. Trunk of a smooth-barked pear tree in early summer, with a sunken 
patch over the places sustaining most severe internal injuries. 
Fig. 42. Detail view of a section taken across the faintest portion of the line 
oc in Fig. 37, showing that normal new wood {nw), arising outside such a line of 
initial injury, may subsequently be killed and discolored. 
Plate XXVI 
Collection of bark-injured and crown-rotted stems, in which the injury was 
accompanied by radial clefts. All of apple except Fig. 48, which is of orange. 
Fig. 43. Apple tree with nearly complete girdle of loose bark (one patch 
opposite) and a radial cleft 17 cm. long. 
Fig, 44. Shows the extent of the loose bark of Fig. 43. 
