PLANT SUCCESSION 187 



tongue (CynngJossiim) , sweet cicely {Osmorhiza) , bed-straw (Galium) 

 beggar's lice {La])pula), and bur grass {Cenchrus) are familiar exam- 

 ples of animal disseminated fruits. 



Another interesting class of fruits that are scattered by animals 

 consists of those that are fleshy or possess a more or less juicy, edible 

 pulp. Such fruits are eaten abundantly by birds and other animals 

 and the seeds are likely to be disseminated. On the other hand, fruit- 

 eating animals do not always facilitate dispersal, since they eat and 

 digest many seeds. Acorns and nuts of various kinds are eaten in 

 large quantities by squirrels. Occasionally nuts that are buried by 

 squirrels are not eaten and so ma}' germinate, but as a means of 

 dissemination this method is, to say the least, very precarious. 

 Ants are dissemination agents of considerable importance in the 

 case of seeds, such as those of blood-root (Sangidnaria) , ginger 

 (Asarum), and the false mermaid weed {Floerkia), which have oily 

 or albuminous appendages. The ants feed upon these appendages 

 and often carry the seeds considerable distances. 



Wading birds often carry seeds in the mud that adheres to their 

 feet. This undoubtedly accounts for the wide distribution of many 

 aquatic plants since such birds often fly for great distances and 

 almost always from one body of water to another. The efficiency of 

 animals as disseminating agents lies primarily in the fact that each 

 species of animal frequents the same type of vegetation most of the 

 time. Animals that live in forests, for example, either stay in the 

 same forest or go from one forest to another so that any seeds or 

 fruits that they carry are likely to be dropped in places that are 

 suitable for their growth. 



Man is a very important agent of dispersal. He acts in the same 

 way as other animals to a certain extent but is more important be- 

 cause of his common carriers. Railroad trains, for example, may 

 carry seeds for long distances and scatter them along the right of 

 way. So true is this that one almost always finds a flora along a 

 railroad that is rich in the number of species. 



119. Plant Succession.— The discussion of the means of dissemina- 

 tion in the preceding paragraphs is enough to answer the question 

 as to where the plants that we see came from and how they happened 

 to find suitable places in which to grow. They came from already 

 existing communities and the seeds of each species were scattered 

 everywhere, but only those that fell into suitable communities were 

 able to grow. The development of plant communities from birth 

 to maturity is called plant succession. This will be discussed at 



