1883.] Means of Plant Dispersion. 1029 
wooly coats of animals. In the allied Bidens, or bur-marigold, 
the awns are downwardly barbed for more efficient action, and act 
on the principle of the fishhook. Let one but walk among these 
weeds in autumn, when the fruit is ripe and ready to be dispersed, 
and the utility of the apparatus at once becomes apparent. 
Another family well represented by burs is the Borragin- 
aceæ. In Echinospermum, or stick-seed, the margin of the 
nutlet is armed with one to three rows of prickles curved at the 
apex. In Cynoglossum, or tory-bur, three species of which are 
found in our Northern flora, the nutlets are covered with these 
barbed and incurved prickles. In regions where sheep are kept, the 
troublesomeness of the tory-bur and beggar'’s lice (C. morisoni) 
are only too well known. 
One of the grasses is furnished with efficient means of dissemi- 
nation by animals, @. e., Cenchrus tribuloides, the sand-bur, growing 
abundantly in waste glact and roadsides, in dry, sandy ground. 
The persistent involucre, enveloping the fruit, becomes dry and 
hard, and is covered with hooked spines, very adhesive to any 
soft object that comes in contact with them. Even some of the 
bearded grasses, like Elymus, with their rough awns, have some 
power of sticking to the coats of animals. 
The agency of animals in diffusing the spores of cryptogamous 
plants must not be omitted. Insects, crawling over these when in 
fruit, must get their bodies well dusted with the microscopic 
spores, and carry them away, as in the analogous case of the pol- 
len of flowers for cross-fertilization. The spores are sometimes 
roughened by minute projections, appearing granulated or even 
spinescent, like the pollen grains of Malvaceæ and many Com- 
positæ, more adequately preparing them to cling to the bodies of 
insects and other animals. Several mosses have these roughened 
Spores, as Aphanorhegma, Pylaisæa velutina, Physcomitrium pyri- 
Jorme, Trichostomum pallidum and others that might be men- 
tioned. That Bacteria and Micrococci are thus carried by animals 
is proved by recent research. When they are found in such vast 
numbers in the air, they must of necessity lodge on the bodies of 
dispersed in this manner. J. B. Schnetzler states “that the dejec- 
tions of oe always contain numerous living Bacteria and 
their germs.” 
* Journal of Royal Mic. Soc., Oct. 1882, p. 658. 
