22 BORTHWICK—ADVENTITIOUS ROOTS AND RELATION © 
- believe that this parenchyma-cone is derived by growth from the 
medullary ray, and that it is an exaggeration of the rudimentary 
cone seen in Plate VIII., Fig. 7. 
The section (Plate VIII., Fig. 11.) is transverse to the medul- 
lary ray as it passes through the wood-body, and being tangential 
to the stem near the periphery of the wood the centre is occupied 
by xylem, and to the right and left of this occurs a narrow strip 
of phloem cut obliquely. In the wood-body the medullary ray 
appears circular in outline. The figure also illustrates how the 
tracheids of the wood have become curved and twisted on their 
passage into the medullary ray. Those tracheids, which lie 
immediately above and below the ray, do not reveal any twisting 
in the section, but that they do bend into the ray is apparent in 
Plate VIII., Fig. 5 ; as they are curved, however, in the median 
plane we merely see them cut at various angles, more or less 
oblique. On the other hand, the lateral tracheids, or those lying 
to the right and left of the ray, show distinctly this incurving and 
torsion, which we would expect to find after an examinatinon 
of Plate VIIL., Fig. 8. The passage of the ray was traced through 
the phloem, whose elements were found to twist the curve into 
the ray, much in the same manner as those of the xylem. The 
bending aside or lateral displacement of the bast-fibres and the 
radial arrangement of the xylem in the developing root was very 
conspicuous in this region. A section made in the cortex of the 
stem and therefore nearer the apex of the papilla shows 4 
surrounding sheath of parenchyma which belongs to the cone 
seen in Plate VIII., Fig. 6. Near the apex of the papilla an outer 
ring of tissue belonging to the cortex of the parent axis becomes 
visible, but it is very narrow, and its cells, which abut on the 
parenchyma-cone of the medullary ray-root, are very muc 
compressed, and the apical meristem of the root occupies the 
greater part of the section. 
Piate VIIL, Fig. 13, illustrates the appearance of a similar out- 
growth formed on Thuja gigantea. The section is transverse to 
the mother-axis and therefore longitudinal to the papilla which © 
is cut in median section. At its apex is seen an undifferentiated 
mass of meristematic cells in which no trace of the central axis- 
cylinder can as yet be detected. Further down, the central 
cylinder appears and its basal connection with the xylem, 
