72 
SEED DISPERSAL. 
hastily leave one place for another. In this way seeds of 
water plantain, sedges, grasses, rushes, docks, arrowhead, 
pondweeds, duckweed, cat-tail flag, bur reed, bladderwort, 
water crowfoot, and many others are transported from 
one pond, lake, or stream, to another. In some cases 
enough of a living plant may be detached and carried 
away to keep on growing. Darwin found on the feet of 
some birds six and three-quarter ounces of mud, in which 
were five hundred and thirty-seven seeds that germinated. 
Mud may be carried on the feet of land animals as well 
as on aquatic animals, not only from ponds and bogs, but 
from the fields where seeds may have accumulated in the 
earth or washed down the slopes. 
45. Why some seeds are sticky. — Some seeds and fruits 
are sticky ; in some instances the mucilaginous substance 
is normally moist enough to adhere to anything that touches 
it, while in other cases it requires to be wetted before it 
will adhere. The seeds of flax, plantain, peppergrass, 
basil, sage, dracocephalum, groundsel, drop-seed grass, and 
many others less familiar, possess this peculiarity. The 
berries of some plants, when fully ripe, burst very easily 
when touched, and some of the seeds are then likely to 
adhere to animals and be carried away. Some berries of 
several plants belonging to the nightshade family have 
this peculiarity, as well as some of the cucurbits. When 
the outer covering of seeds of water lilies, arums, and 
others are broken, the gummy secretion is very likely to 
adhere to the feathers, or fur, or feet of animals. A num- 
