MELANTHACE/E FROM THE GENETIC STANDPOINT. 149 
a reason for creating a new genus in this case. A. angustifolium is smaller, 
and it differs from A. muscetoxicum in its narrower leaves and smaller 
flowers, in addition to certain minor differences, as in the shape of the sepals 
and relative length of the stamens. But intermediates in certain localities 
occupied by both species make it very difficult to draw any definite line 
between them. Indeed, the two forms are by no means always easily 
separated. There is a possibility of tetraploidy here. Amianthium, 
Xerophyllum, and Stenanthium are all examples of essentially bitypic genera, 
in which the two species differ chiefly in having broad or narrow leaves. 
This type of dimorphism is a common one in the plant kingdom, and probably 
has some special explanation which is at present obscure. Schanocaulon 
dubium and S. Drummondii form a similar pair (see p. 150). A. texanum 
differs from A. angustifolium in its larger size, broader leaves, large 
compound panicles, and decidedly yellowish flowers, the perianth-segments 
being oval, 4-5 mm. long. It resembles Stenanthium, but the panicle is 
much smaller and less branched and the perianth-segments not narrow and 
acuminate. The differences between Chamelirium and Amianthium will 
appear in the following comparative table :— 
Chamelirium. 
Bitter, tuberous rootstock, 
Basal leaves short, spatulate, tapering into 
a petiole; stem-leaves lanceolate. 
Flowers small, dicecious, in a long, narrow, 
bractless, spike-like raceme. 
Perianth-segments  linear-spatulate, 1l- 
nerved, withering-persistent. 
Anthers subglobose. 
Ovary oblong or obovate, somewhat 
grooved. 
Styles short, stigmatic along the inner side. 
Capsules slightly 3-lobed, ellipsoid. 
Seeds 6-12 in each cavity, linear-oblong, 
broadly winged at both ends, narrowly 
winged at the sides. 
Amianthium. 
Ovoid-oblong coated bulb. 
Basal leaves numerous, long, linear, and 
blunt; stem-leaves few and short. 
Flowers perfect, in a dense terminal raceme. 
Perianth-segments obtuse, persistent. 
Anthers reniform, stamens inserted on the 
base of the sepals. 
Ovary ovoid, with 3 divergent lobes. 
Styles subulate. 
Capsules 3-celled, dehiscent above the 
middle. 
Seeds 1-2 in each cavity, ovoid, reddish 
brown. 
The diccism of Chamelirium and the bulb of Amianthium separate 
these genera much more widely than their other morphological features, 
which show many resemblances. Diccism has been attained independently 
a number of times, but we do not know whether it is usually accomplished 
by one step from hermaphroditism, or whether the passage is more gradual 
through moncecism and polygamodicecism *. The bulbous condition has also 
* The converse change, from diccism to hermaphroditism, seems to have occurred much 
earlier in the evolution of the flower, 
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