CROWN-ROT OF FRUIT TREES: HISTOLOGICAL STUDIES 483 
black). A portion of the continuation of this ray in the wood is also 
dead, although its cambial portion is still alive. In the next ray to 
the right, the outer portion is dead and that in the inner phloem and 
cambium is alive; but its extension into the wood cylinder is dead- 
and discolored. The phloem and cambium tissues lying between 
these rays are mostly dead, but scattered living cells occur singly 
or in small groups. The phloem tissue between the two rays toward 
the right of the figure are in much better condition, containing only 
a few scattered groups of dead cells. It is worth noting that toward 
the right of the figure the main line or sheath of injury runs through 
the outer phloem, while toward the left it affects chiefly the cambium 
and inner phloem. However, even the most severely injured sheath 
has living cells interspersed among the dead and collapsed ones. 
In Fig. 5 such is not the case; here the sheath of injured tissue involves 
the cambium and inner phloem on the left; at about the middle of 
the figure it bends suddenly and proceeds through the phloem, leaving 
the cambium alive except for occasional groups of injured cells. 
In this instance the sheath of most severe injury contains few living 
cells, thus practically eliminating all living connection between the 
wood, or its living fringe of cambium, and the bark proper outside 
the injured sheath. Fig. 6 shows a comparable condition excepting 
that more, dead cells are scattered among the living tissues. In this 
instance the broad ray near the center is dead in both bark and 
wood, and on the left the entire cambium and the inner phloem, with 
the exception of a few cells, are collapsed. The outer cortex shows 
many dead cells. Fig. 7 gives a better idea than the others of the 
injury occurring in the inner bark: here the cambium and inner 
phloem as well as the rays and much other phloem tissue are dead 
and more or less collapsed. In the cambial region near the left, 
however, is a group of two or three living cells with irregular outlines. 
These cells, as well as those of certain groups in Figs. 4 and 5, are 
apparently enlarged, although the apple trees from which this material 
was cut seemed perfectly dormant at the time. It appears likely that 
this represents the beginnings of spring growth and regeneration, 
brought on early as a response to the wound stimulus. In Fig. 8 
occur two lines or sheaths of severe injury, one of which involves the 
cambium and the other the outer phloem. Neither of these zones 
is made up wholly of dead cells, so that the sheath of living phloem 
between them is not entirely without living connection with the wood 
