Sio 
Lee. — Observations on the 
upper part of the latter, the extreme lateral bundle on either side fuses with 
its fellow from the other cotyledon, and in pursuing its way down the 
hypocotyl the resulting strand bifurcates, the protoxylem becoming external 
during the process. 
Thus a tetrarch rcot is formed in which, as one might expect in so 
large a seedling, there is at first a large pith. The smaller lateral bundles 
of the cotyledon continue unchanged for a long distance in the hypocotyl. 
Finally, however, owing to the decrease in size of the latter as it passes 
into the root, the whole of the vascular tissue becomes arranged nearer the 
centre, and the bundles, fusing laterally, form a continuous ring of xylem 
Diagram 5. Heliopsis laevis. Seedling A. 
and a ring of phloem which is only broken where it passes the protoxylem 
groups. 
The rearrangements are thus initiated in the seed-leaves, and the region 
of transition is very elongated. 
Heliopsis laevis , Pers. The seedlings were of the small, slender type, 
but the seed-leaves were long and rather fleshy, and also were unequal in size. 
Seedling A. In the cotyledons there is the usual branching and 
re-fusion of the vascular bundles, as a result of which six strands (three from 
each seed-leaf) pass into the short cotyledonary tube (Diagram 5, 1). The 
two in the cotyledonary plane are very large. Each of these bifurcates, the 
xylem assuming the form of a flat ribbon with the small protoxylem elements 
