192 
Hill and de Fraine. — On the 
The bundles a , £, and c underwent bifurcation of their vascular elements, 
and rotation of the protoxylems as described for Tsuga canadensis and 
illustrated in Diagram 1. The strands, however, performed differently. In 
the upper part of the hypocotyl, d converged towards a (Diagram i,Fig. 2), 
and at the same time a rearrangement of the xylem elements began which 
ultimately resulted in the protoxylem occupying an exarch position : the 
phloem of d showed no signs of bifurcation but fused with the adjoining 
portion of the bast of a (Diagram 1, Figs. 3 and 4). At lower levels of the 
hypocotyl the protoxylem of d gradually made its way through the inter- 
Diagram i. Abies sibirica. In this, and in all the following text-figures, the protoxylem is 
indicated by black areas, the metaxylem by dots, and the phloem by shading. 
vening metaxylem elements, and effected a junction with the same tissue of 
a (Diagram i, Figs. 4-6). A triarch root-structure was thus attained. 
Different views may be held regarding the features described for this 
particular individual : the seedling may represent a late stage in the splitting 
of one seed-leaf to form two cotyledons, but a comparison with what obtains 
in Cupressus torulosa 1 shows important and obvious features of difference. 
The bundles a and d of Abies sibirica do not converge, and by a compara- 
tively simple sequence of events give rise to one pole of the root as in the 
case of Cupressus torulosa ; in the seedling of Abies sibirica , the phloem of 
a bifurcates and one portion accompanies the bast of d to effect a junction 
1 Part I, Annals of Botany, 1908, p. 700, Diagram 4. 
