Arum macu latum from the Seed . 409 
second leaf is quite rudimentary. Yet not only are the 
bundles of the cotyledon well developed, but three pro- 
cambial strands are already indicated in the first leaf. A little 
lower down in the axis these strands are better defined, and 
the structure of the first internode is perfectly clear. The 
five cotyledonary traces 1 form a peripheral circle ; within 
them are the three plumular bundles which correspond in 
position to the traces of the first leaf. But this, as we have 
seen, is the typical structure of the first internode in much 
older tubers. 
Complete series of sections can be cut through the axis in 
seedlings of this age without difficulty, and we possess five 
such sets of transverse sections. All of them begin near the 
base of the stem-bud and are continued through the tuber 
into the primary root. Three series are cut through seedlings 
of the age shown in Fig. 1 ; two through rather older 
specimens, corresponding to Fig. 2. The main features of the 
transition are the same in all these cases, though no two are 
alike in every detail. Figs. 14 and 15 are drawn from two 
sections cut from the same axis. 
The diagram (Fig. 13) shows that the eight bundles of 
the first internode form three groups in the succeeding node. 
But the process is not nearly so symmetrical here as in the 
second and third nodes. We have five traces entering the 
central cylinder in place of three, and the transition to root 
structure begins in the node itself. No part of the hypocotyl 
therefore shows the characters of a true stem. It will perhaps 
be easier to appreciate the difficulty of interpretation if we 
follow the bundles from the first internode through the 
succeeding node, and the hypocotyl into the primary root 
in a single instance. We will choose that seedling from which 
Figs. 14 and 15 are drawn. 
It has already been stated that there are eight bundles 
in the first internode. The five cotyledonary traces lie near 
the periphery, while the three plumular bundles form a smaller 
1 In Fig. 14 the cotyledon shows six bundles. The sixth is more slender than 
the others, and disappears lower down. This is a common anomaly. 
