160 DR. R. R. GATES: A STUDY OF NORTH AMERICAN 
any extinction having taken place between these genera. There is, for 
example, no gap between the species of Tozicoscordion and those of Anticlea. 
In the absence of such a gap, the separation of these two genera is by 
no means a sharp one, and indeed is only justifiable on grounds of convenience. 
Since Z. glaberrimus is confined to the south-eastern States, while Towicoscordion 
and Anticlea cover a much wider area, it may perhaps be assumed, considering 
also the other relationships of Zigadenus, that its origin took place relatively 
recently. On the other hand, it is possible that it may be a survivor of a 
group similar to the present Anticlea. 
The distinctions between species in Anticlea and Toxicoscordion are founded 
chiefly upon such features as the shape of the perianth-glands, the size and 
shape of sepals and petals, whether clawed or clawless, the width of leaves, 
and the nature of the raceme. These differences are for the most part not 
sharply marked presence and absence characters, but tend to be quantitative 
and continuous. This makes the discrimination of species difficult. The 
two genera are, in fact, in rather a chaotic condition, owing partly to the 
nature of the specific differences, partly to their variability, and partly to the 
description of a number of new species on a rather slender basis and from 
insufficient material to determine the range and manner of variation of the 
various forms. 
In the preceding pages I have merely assembled the species, some of which 
will very likely be reduced to synonymy, but the genus can only be adequately 
treated after some botanist has made a careful study in the field. 
We have already concluded that the present Zigadenus represents an 
ancestral condition from which Oceanorus, Anticlea, and Toxicoscordion were 
derived. On the other hand, Zigadenus has clearly led to Melanthium, and 
Melanthium to Veratrum through the loss of the glands on the perianth- 
segments. Hence we may conclude that Zigadenus is the oldest genus in 
this section of the Melanthacez. Presumably it and Stenanthium are 
descended from a common ancestor, Zigadenus having developed the pairs of 
glands on the perianth-segments and also the claws on these segments, How 
these two features developed, we have at present no means of knowing, but 
there has probably been considerable extinction between the present genera 
Zigadenus and Stenanthium. 
16. MELANTHIUM, Clayt., ex Linn. 
1. MELANTHIUM VIRGINICUM, Linn. Sp. Pl. (1753) 339; Lamk. Encyc. iv. 
(1823) 24, t, 269. f. 1, 
M. letum, Kinn, ex Kunth, Enum. Pl, iv. (1843) 195. 
M. biglandulosum, Bertol. in Mem. Acc. Sc. Bologn. ii. (1850) 316. 
Asphodelus elatior Floridanus gramineis foliis, floribus parvis et herbaceo-pallescentibus, 
Pluk, Amalth. (1705) 40, t. 434. f. 8, 
