262 



General Botany 



Seeds are transported by animals in several ways. They may be 

 inclosed in fruits like the burdock, cocklebur, and Spanish needle, 



and become entangled in the 

 fur coat of the animal. They 

 may be eaten and, due to im- 

 pervious seed coats, survive the 

 digestive juices of the animals. 

 They may be carried and buried 

 by squirrels, ground squirrels, 

 and gophers. The walnut, but- 

 ternut, and hickory nut have no 

 other means of being carried 

 away from the parent plants. 

 Small seeds that have fallen on 

 the muddy banks of ponds and 

 streams may be carried by water 

 birds in the mud that clings to 

 their feet. The mistletoe pro- 

 duces seeds with an outside 

 sticky coat. These also are said 

 to be spread to other trees by 

 adhering to the feet of birds. 

 Finally, the greatest of all trans- 

 porters of seed are human be- 

 ings. Wherever man goes there 

 follows shortly in his trail a host 

 of weeds. His ships carry them 

 across the oceans, and his railroad trains scatter them over 

 the land. The continual shipment of agricultural and horti- 

 cultural products of necessity leads to the spread of seeds of 

 various other plants that grew with them. More than half of 

 our weeds have been introduced from Europe in this way. 



Economic importance of seeds. Seeds and grains supply the 

 most concentrated foods derived from plants. They provide 



Fig. 169. Development of mangrove 

 seedlings. This small tree grows on soft 

 mud flats in the tropics and semi-tropics. 

 The seed {A and C) germinates while 

 still attached to the tree and forms an 

 embryo a foot or more in length. The 

 embryo finally drops endwise like an 

 arrow into the mud below and starts a seed- 

 ling (D). 



