SEEDS AND FRUITS CARRIED BY ANIMALS 85 
Darwin took 3 tablespoonfuls of mud from beneath the water at 
the edge of a pond and kept it in his study until the seeds con- 
tained developed into plants. From this small amount of mud, 
he obtained 537 plants which represented a number of species. 
From this it is evident that the 
mud, carried on the feet and legs 
of water birds, may be the means 
of distributing many seeds. 
The fruits and seeds of many 
plants have spines or small hooks 
by which they become attached 
to passing animals and are carried 
far and wide. Some familiar ex- 
amples are the burs of Burdock, 
Cockle Bur, and Sand Bur, and 
the hooked and spiny fruits of the 
Buttercups, Wild Carrot, Beggar’s 
Lice, Tick-trefoils, Beggar-ticks, 
and Spanish Needles. They catch Bid. BTR Chickadee carving 
in the wool, manes, and tails of fruit. From Bulletin 4, lowa Geo- 
stock and in the clothing of man, logical Survey. 
and are carried from one pasture 
to another or from one farm to another. Live stock are impor- 
tant agents in distributing plants on the farm. The seeds of 
the Mustards are mucilaginous when wet and, by sticking to the 
feet of animals or the shoes of man, are carried to new situations. 
(Fig. 88.) 
Many plants owe their distribution to man more than to any 
other agent. The railways, connecting all of the states and 
reaching from ocean to ocean where they connect with steamship 
lines from across the seas, are responsible for the wide distribution 
of many plants. For example, the seeds of a number of weeds 
are shipped across the country with grain and other farm seeds, 
and also in hay, bedding, packing, in shipments of fruit, and 
in the coats of live stock. They fall from the cars as the train 
travels, and seed the right-of-way where the plants first appear 
and then later spread to the surrounding fields. The railways 
are responsible for the wide distribution of Russian Thistle, 
Prickly Lettuce, Canada Thistle, and Texas Nettle, which first 
appear along the railway and later spread to the surrounding 
