SEEDS. 17 



the seeds are conveyed to some distance from the plant on 

 which they are produced. By this means they 

 are less likely to come into as close competition 

 with each other as if they grew up together around the 

 parent plant; they are also brought into other conditions 

 of soil and surroundings, and the chances for cross-fertil- 

 ization are greater, which, as we shall see, is often a 

 marked advantage. Accordingly it is found that a variety 

 of structures exist that are directly adapted to the dis- 

 semination of seeds. Thus many seeds are distributed 

 by the action of the wind. These are most frequently 

 light in weight and provided with appendages in the form 

 of wings or hairs, such as those of the catalpa, poplar, 

 milkweed, and many others. Seeds distributed by animals 

 are often concealed within brightly colored or otherwise 

 attractive fruits ; in other cases they are provided with 

 hooks or other appendages by which they become attached 

 to the wool or hair of various animals, and the seeds of 

 many water-loving plants are carried in the mud that 

 adheres to the feet of aquatic birds. The seeds of still 

 others are washed by oceanic currents to the shores of 

 distant islands or continents, and, finally, the agency 

 of man, both intentional and unintentional, becomes a 

 potent factor in the distribution of plants. 



By these and other agencies the forms that constitute the 

 vegetation of the earth have come to occupy the places in 

 which we now find them, and it becomes for every species 

 that we meet a fascinating and often intricate problem to 

 endeavor to ascertain how it came to be where it is. 



It is plain that from the time they leave the mother plant 

 to the time of germination, seeds are exposed 

 to numerous dangers, and that they require pro- 

 tection. This is afforded in part by the shape of the seed, 



