1913] CHRYSLER—PHLOEM OF ABIETINEAE 4I 
The cells in question apply themselves to the side of the ray, and as 
cambial activity in the radial group slackens, this activity is 
reStricted to the border of the ray, thus changing the ray from a 
simple one consisting only of parenchymatous cells to a ray provided 
with marginal cells. With fig. 5 may now be compared fig. 1, 
which shows the same mode of origin for the marginal cells of the 
phloem region of the ray in P. Strobus. Observations have been 
made on representatives of the hard and soft pines, including the 
nut and foxtail pines, and appearances similar to fig. 5 have been 
found in all, when roots of appro- 
priate age were examined. Be oe 
Regions where two rays lie near | | 
one another in the vertical plane 
present appearances which may 
readily be explained in the light of 
what has been said of the radial 
plates. Fig. 6 shows such a region 
in a 6-year root of P. Strobus. In 
the upper part of the figure is a 
ray which on one margin is desti- ; ro oen 
tute of erect cells, and on the other pie ‘ni ae 
(lower) margin is provided witha  @ FE POOL 
fringe of much elongated cells el # MCI (C Val 
which soon merge into a group of 8 pied beep  FF1 
prismatic cells forming a radial pies mi ad a it 
plate of tissue by means of which marginal cells; 275. 
the ray shown is connected with 
another which lies below the area covered by the figure. These 
cells of the “radial plate” show precisely the same histological 
features as those previously described, such as the sieve areas which : 
are here shown. At the extreme left of the figure is a row of phloem 
parenchyma cells, which are easily distinguished from the cells of 
the radial plate by the starchy contents and swollen shape of 
the former. 
Further transition stages are shown in fig. 7, from a 5-year root 
of P. Strobus, which represents cases where two rays are closer than 
those in fig. 6. Almost from the time of their formation from 


FRR Pee 
