36 Sargcint . — Theory of the Origin of Monocotyledons 
Yucca gloriosa. There are four bundles throughout the 
length of the cotyledon : within the seed, and again in the 
lower part of the sheath, the two median bundles approach 
each other and their protoxylem groups unite. The structure 
of the cotyledon is then precisely that found in Y. aloifolia. 
The four cotyledonary traces are continued into the 
hypocotyl, where they are joined by two or three from the 
plumule. All the traces behave alike during the transition : the 
xylem groups branch to right and left, and adjacent branches 
unite with each other. The root is either hexarch or heptarch. 
Dracaena Draco is the only species I have examined from 
this genus. 
The seedling is very robust : the pi annular bud is developed 
early, and the primary root is particularly long, thick, and 
persistent. The cotyledon is merely a sucking organ, and 
it remains for a long time within the large seed, never appear- 
ing above ground. 
There are seven bundles in the neck of the cotyledon where 
it emerges from the seed. Six are arranged in pairs to form 
three double bundles — each with a common protoxylem 
group. The seventh is single. This structure is continued 
into the sheath. As they descend, the three common proto- 
xylem groups become more and more external. In this way 
the transition to a root-structure begins before the cotyle- 
donary traces enter the hypocotyl. 
The plumule contributes many traces to the hypocotyl — 
six to eleven in the seedlings I have examined — and the 
transition to a root- structure is very far advanced before they 
enter it. Both in cotyledon and plumule it proceeds — as 
in Yucca — according to Van Tieghem’s type i. The result- 
ing root is polyarch. I have found as many as eighteen 
phloem and xylem rays in it. 
The four last species have been described at some length, 
because they display characters common to most of the arbor- 
escent forms which belong to this and allied orders. The 
primary root is persistent, and the insertion of the plumule 
