1 6 Sargant . — Theory of the Origin of Monocotyledons 
directions. The two upper branches (px 2 and px\ in Fig. 3) 
unite, while the median branches (px ± and px 4 ) maintain their 
identity. The lower branches (px 3 and px'. d ) are separated 
by the lowest phloem group, which is that derived from 
the two lateral branches. The xylem of lj fuses with the 
branch px 3 , and the xylem of 1 2 with px\. These changes 
when accomplished produce a pentarch root- stele. 
Of the two other seedlings cut, one agrees in every point 
with A 4 . The other begins in the same way, but one of the 
median branches of protoxylem is suppressed after it has been 
formed, which leads to the asymmetrical formation of a tetrarch 
root. This is clearly anomalous. 
The lateral bundles of Muscari atlanticum play a more 
important part in the process of transition than they do in 
Hyacinthus romanus . They add a phloem group to the stele, 
besides contributing elements to two others and to two proto- 
xylem groups. The division of the two main bundles takes 
place exactly as in Albuca. 
Muscari armenaicum . The cotyledon contains four bundles 
almost throughout its length. Two of these are more massive 
than the others. Each of the two slighter bundles gives off 
a branch in the upper part of the sheath. Below this level 
we find two main bundles and four lateral ones in the sheath. 
But the two supplementary bundles reunite at the first node 
with the bundles from which they arose, and the transition 
from stem to root takes place with four traces only in the stele. 
Sections from the transitional region of two of the three 
seedlings cut are drawn in Figs. 5, 6, 7, and 8. The third 
seedling, A 4 , is younger than the others, and the lateral traces 
are poorly developed. The process of transition, however, is 
clear, and it is precisely that just described for M. atlanticum . 
The transition in seedling A 3 differs from this, and that of 
seedling A 5 is unlike either. 
In seedling A 3 one of the two main bundles (M x ) behaves in 
the characteristic way. Its xylem branches in three directions : 
its phloem bifurcates. But in the second main bundle (M 2 ) 
