Page:First course in biology (IA firstcourseinbio00bailrich).pdf/207

 seeds are transported. Nuts are buried by squirrels for food; but if they are not eaten, they may grow. The seeds of many plants are blown on the snow. The old stalks of weeds, standing through the winter, may serve to disseminate the plant. Seeds are carried by water down the streams and along shores. About woolen mills strange plants often spring up from seed brought in the fleeces. Sometimes the entire plant is rolled for miles before the winds. Such plants are "tumbleweeds." Examples are Russian thistle, hair grass or tumblegrass (Panicum capillare), cyclone plant (Cycloloma platyphyllum), and white amaranth (Amarantus albus). About seaports strange plants are often found, having been introduced in the earth that is used in ships for ballast. These plants are usually known as "ballast plants." Most of them do not persist long. 185. Plants are able to spread themselves by means of the great numbers of seeds that they produce. How many seeds may a given elm tree or apple tree or raspberry bush produce?