32 Sargant. — Theory of the Origin of Monocotyledons 
lonicum , A. angulosuni) as well as to Bloomer ia aurea and 
Brodiaea lactea . In the two species last named the bundles 
of the cotyledon are distinct throughout. Indeed, the cotyle- 
donary sheath of Bloomeria , with its two distinct and rather 
massive bundles, recalls the symmetry of the Asphodeleae. 
Milla biflora also possesses two distinct bundles in the 
cotyledon, which are less reduced during the transition than 
those of Allium. A small plumular trace also enters the 
hypocotyledonary stele, and each of the three xylem groups 
branches to right and left. The phloem remains in situ. 
A triarch root is formed according to Van Tieghem’s type i. 
5. Tribes : Veratreae, Uvularieae, Medeoleae. 
Two species from the Veratreae have been examined, 
Zygadenus elegans and Veratrum nigrum ; one species from 
the Uvularieae, Tricyrtis hirta ; and one from the Medeoleae, 
Trillium grandiflorum. 
In one feature these four species resemble each other. The 
cotyledon contains a single and rather massive bundle, placed 
in the position of a midrib, and sometimes accompanied by 
lateral bundles. This central bundle opens out in the neigh- 
bourhood of the first node into a double trace resembling 
that of Allium. 
Zygadenus elegans. The cylindrical cotyledon contains 
but one bundle throughout: a section near the top hardly 
suggests a double structure in the phloem (PL V, Figs. 7 
and 8), but it is clear lower down (Figs. 9 and 10) and 
also throughout the transition. The plumular bundles 
which take part in it separate into two branches : in PL V, 
Fig. 11 these are seen advancing to meet the cotyledonary 
trace exactly as in Allium (cf. Fig. 3). 
The phloem groups of the cotyledonary trace are now 
quite distinct, and separated from each other by the whole 
xylem. The xylem itself is in two masses, between which 
