1883.] Means of Plant Dispersion. 815 
course, since they are able to pass over them. The way in which 
the scales of the floral involucre open, facilitates the process. 
When green they are more or less closely appressed to the head 
of flowers ; when ripe they become dry and spread in a horizontal 
plane, or become reflexed. This exposes the fruit to the ready 
access of the wind, and it is easily lifted from its seat on the 
receptacle. 
In the valerians, two species of which are found in our limits, 
Valeriana edulis and V. sylvatica,a modified calyx also serves 
this purpose. Being persistent and coherent with the one-celled 
and one-seeded ovary, its limb. divides into several plumose bris- 
tles, much like a pappus; these, rolled inward in the flowers, un- 
roll and spread as the fruit matures. 
Among the endogens are found a few of these equipments. In 
Typha, the common cat-tail rush, the ovaries are surrounded with 
bristles, making the abundant down of the fruit, and adapting it 
to wind dissemination. 
In the sedge family are some examples of fruit adjusted to this 
end, principally in Eriophorum, or cotton-grass, and in two species 
of Scirpus, S. dineatus and S. eriophorum. Three species of Erio- 
phorum are common about Lake Michigan (Æ. virginicum, E. poly- 
Stachyon and E., gracile) in marshes and wet prairies, and may 
easily be detected among the surrounding plants in summer and 
early autumn by their cottony heads. The bristles which form 
the perianth, generally short in other genera and species of this 
family, lengthen greatly in the cotton-grass, in some cases to an 
inch, becoming enlarged and numerous. The construction in 
irpus is similar but not so marked. 
The beards and awns of grasses will, to some extent, serve the 
same purpose. Such as have them possess an instrument for 
catching the wind, and the grain is likely to be more effectually 
Scattered than in the case of those devoid of them. The com- 
mon reed (Phragmites communis) has the rachis of the spikelets 
of its ample panicle prominently bearded with soft hairs just be- 
low the spikelets, which are easily detached when ripe. The 
whole appearance is like a plume, and either as a whole or in 
Parts is a light object that may be blown about by the wind. In. 
Calamagrostis and Erianthus, there is an analogous arrangement. . 
The spikes of Hordeum jubatum, or squirrel tail grass, of Setaria, , 
Gymnostichum and Andropogon are also aided by their hairs 
