82 SEEDS AND FRUITS 



tacle; (3) ovary with perianth or bracts forming a husk; (4) ovary 

 with calyx forming hairs or spines; and (5) a number of single 

 fruits with the modified leaves and floral 

 axis of the flower group. A fruit may 

 be defined as one or more ripened ovaries 

 either with or without closely related 

 parts. 



Dissemination of Seeds and Fruits 



Dissemination has to do with the 

 scattering of seeds from the parent plant. 

 Sometimes the seed is transported naked, 

 but often it is transported enclosed in 

 the fruit or with some larger part of the 

 plant. 



The necessity for dissemination is ob- 

 vious, for if the seeds of a plant were to 

 FIG. 84. The dry coiled germinate where formed or on the ground 

 fruits (pods) of Alfalfa directly beneath, the resultant conges- 

 (Medieago sativa). From tion would prevent the normal develop- 

 Farmers' Bulletin 895, U.S. ment o f any of the p l ants . Green 

 Sept. of Agric plantg mugt haye sunlight and air? and 



this means that they must have room. 



Of course seeds and fruits are not the only means by which 

 plants spread. Many Seed Plants have an additional means in 

 either spreading stems or roots which give rise to new plants as 

 they spread farther and farther from the parent. The Straw- 

 berry depends mainly upon its runners, and the Quack Grass 

 much upon its underground stem as a means of spreading. Pop- 

 lars, some fruit trees, and Canada Thistle are well known to 

 spread by means of sprouts arising from their roots. Most plants 

 which do not have seeds spread by means of spores which in some 

 cases seem to be a more efficient means than seeds are. For 

 example, Wheat Rust, a disease which spreads very rapidly, is 

 spread by spores. 



In the dissemination of seeds and fruits, wind, water, and ani- 

 mals are the chief agents. In a few plants there are explosive or 

 spring-like mechanisms which throw the seeds. 



Seeds and Fruits Carried by Wind. The wind is one of the 

 most important agents in the distribution of fruits and seeds. In 



