408 Scott & Sargant . — On the Development of 
phloem forms a complete circle. This xylem-girdle is 
thickened at certain points, and on these the central cylinders 
of the roots are inserted. 
Returning to our younger stem (Fig. 4), we pass downwards 
from the third node into the second internode. In this the 
bundle / has disappeared, for one of its branches has fused 
with / 3 , the other with y. Throughout the second internode 
we have, as shown in Fig. 12, three bundles in the central 
cylinder which are the direct continuation of the traces from 
the second leaf, a, / 3 , y. Surrounding these we have the traces 
of the first leaf, A, B, C, and in a peripheral circle the cotyle- 
donary traces 1-5. In the succeeding node — the second of 
the young stem — the traces A, B , C bend inwards to the 
central cylinder. The lateral bundles B and C fuse with the 
lateral bundles (3 and y. a forks to right and left, and we 
again have an incomplete vascular girdle formed. This time, 
however, it is the xylem of A which is distinct from the rest. 
The two branches of a ultimately fuse with B and C. Thus 
on entering the first internode there are only three bundles 
within the ring of cotyledonary traces. Here, however, the 
series of sections which we have been following breaks off. 
A diagram (Fig. 13) can easily be constructed from other 
examples to show what will take place in the coming node. 
But it will be more convenient to consider its structure in 
detail when we deal with the transition from stem to root. 
This transition begins almost before the formation of the 
first node, and continues throughout the short hypocotyl. 
Transition from Stem to Root. 
The transition from stem to root in the hypocotyl of Arum 
maculatum can be most satisfactorily followed in very young 
seedlings. Even at the age shown in Fig. 1, all the bundles 
of the first internode are clearly differentiated. Fig. 14 is 
drawn from a section passing through the stem-bud of the 
youngest seedling in our possession. Only two leaves and 
a growing point are found within the cotyledon, and the 
