TO BIRD’S-EYE FORMATION IN THE WooD OF TREES. 21 
The origin, method of growth, and morphology of those struc- 
tures is illustrated by the accompanying series of figures. 
The first changes, which ultimately lead to the formation of 
those outgrowths, are found to take place in a medullary ray, 
the cells of which become very rich in protoplasm and develop 
large conspicuous nuclei. They then begin to divide by radial 
walls, so that the ray gradually increases in breadth till it ulti- 
mately loses its flattened plate-like character and becomes more 
like a cylinder in shape. 
Plate VIII, Fig. 7, shows a ray in which this process had 
begun two or three years previously. It appears as an attenuated 
wedge with the thin end towards the pith, becoming gradually 
broader on its outward course through the xylem and dilating 
in the extra-xylar and cortical portion of the stem in a club-like 
manner. Throughout its whole length it consists entirely of 
parenchyma-cells. Those of the swollen apex are in an active 
state of division and growth, and are readily distinguished from 
the cells of the surrounding phloem and cortex by their large 
well-marked nuclei. 
A further stage of development is shown in Plate VIIL., Fig. 8. 
Here may be seen curving into the ray the cells of the wood- 
cambium which proceed to lay down, in a centrifugal manner, 
tracheids, the long axis of which is in a plane more or less at 
right angles to that of the wood-body. The first trace of this 
in-arching of the cambium may be seen in Plate VIII., Fig. 7, to 
the right of the ray where it passes through the cambium-zone, 
From this stage onwards the central portion of the ray consists 
of parenchyma plus tracheids. : 
In Plate VIII., Fig. 6—an older papilla in transverse section— 
the parenchyma-cone has become much larger, the central cylinder 
which is in connection with the wood-body of the stem makes a 
downward curve towards its apex—see Plate VIII., Fig. 5—hence 
this portion is not included in the section, but the preparation 
serves to illustrate how the parenchyma-cone has developed and 
has almost totally obliterated the cortical cells lying in its line of 
growth. It also indicates that the phellogen does not take any 
part in the formation of the protuberance. Whether the phloem- 
parenchyma participates in its formation or not I cannot say, but 
from an examination of all my sections I am strongly inclined to 
