70 PLANT MIGRATION 
entangled in the hair or fur of passing animals. Ex- 
amples will occur at once to the reader, as this char- 
acter occurs in the case of many familiar plants, 
such as Burdock (Arctium), Enchanter’s Nightshade 
(Circea), Avens (Geum), and so on. Without doubt 
these hooked fruits often secure a wide local dispersal 
by the aid of cattle, sheep, rabbits, and so on: the 
state of one’s trousers or stockings after walking the 
autumn woods is often very suggestive in this regard. 
Again, herbivorous quadrupeds eat seeds in quantities, 
many of which are capable of germination after 
passing through the animal’s body. But while the . 
dispersal obtained by such means may often aid in 
spreading a species over a tract of land, it does not 
generally aid in the crossing of barriers, such as 
mountains or sea, on account of the limitations to the 
movements of such animals. To arrive at a true 
estimate of the importance of the animal kingdom in 
regard to plant migration, we have to study the 
movements, habits, and food of birds, to whose 
wanderings neither mountains nor seas set a barrier. 
Seeds are carried about by birds in two ways—by 
becoming attached to their feathers or feet, or by 
being eaten and subsequently ejected. The first case 
belongs to the class of phenomena which we have just 
been considering, save that the smooth plumage of 
birds, and their frequent preening of their feathers, 
tends to keep their coats free from extraneous 
material. But at least in wet weather minute seeds 
must often cling to feathers and to feet, and mud 
which may contain seeds may easily be present on a 
bird’s toes during flight. More important is the ques- 
tion of endozoic dispersal—where seeds are trans- 
