90 FRUITS AND SEEDS 



Carried by Wind. We have all observed the dispersal of 

 seeds by means of the wind. Of course, strong air currents 

 will carry light seeds for great distances, but many seeds have 

 special structures which are very important in this work. The 

 maple, ash and elm have membranous wings, or outgrowths by 

 which the wind carries them. These outgrowths are a part 

 of the ovary. The dandelion, lettuce, thistle and many other 

 plants have seeds which are enclosed in the ovary (achenes), 

 on which is developed a downy outgrowth serving as an air 

 float, a sort of balloon or parachute. The seeds of the milkweed 

 bear a superficial resemblance to those of the dandelion, but are 

 quite different. You will recall that the dandelion is an inde- 

 hiscent fruit, while the milkweed is dehiscent. The outgrowth 

 on the former is from the ovary; on the latter from the seed 

 coat. Some plants, especially weeds, of which the tumble weed is 

 the most striking example, will break loose and be carried by the 

 wind for great distances, distributing their seeds as they travel. 



Carried by Man and Animals. The lower animals are the 

 involuntary carriers of many seeds, and man, the highest of 

 the animals, is both an involuntary and a voluntary carrier. 

 The seeds of many fruits will pass through the alimentary canal 

 of animals unharmed and will grow if dropped in suitable 

 places. Squirrels and other animals bury nuts and other seeds 

 which grow ; while birds accidentally drop the seeds of cherries, 

 berries and other fruits, here and there. Burs and many other 

 seeds have spines or hooks by which they cling to animals. Man 

 carries many seeds in feed and bedding for himself and live 

 stock, in packing materials, and in grain for various agricultural 

 and commercial purposes. The shipping of grain and grass 

 seeds from country to country has been the means of introduc- 

 ing many of our most troublesome weeds. 



Seeds Thrown. Many plants have peculiar devices by 

 which seeds are thrown for considerable distances. The touch- 



