208 



PLANT SUCCESSION 



bers of seeds and fruits fall within a few hundred feet of the parent 

 plants so that the greater the distance of the feeder vegetation from 

 the new area the less likely is migration to it to be attained. For 

 this reason certain stages in the succession, those for which feeder 

 vegetation is near by, are likely to develop much more rapidly than 

 those that must be fed from a greater distance. Furthermore, the 

 topography of the intervening area indirectly influences migration. 

 High hills or a forest may act as barriers which more or less effectu- 

 ally prevent migration where it would take place quickly over a 

 level, unbroken area. 



Fig. 92. — Coprinus comatus. 



One of these mushrooms may produce more than 

 5 billion spores. 



Migration must be followed by ecesis before invasion can be said 

 to have been completed. Ecesis is the establishment of a plant in a 

 new home after it has migrated. It consists of three processes, ger- 

 mination, growth, and reproduction. 



In the great majority of seeds there is a period of arrested de- 

 velopment after the embryo has been formed during which the seed 

 is said to be in a state of dormancy. At the end of the dormant 

 period growth is resumed and the seed is said to germinate. Dor- 

 mancy and germination are also characteristic of other propagating 

 bodies such as bulbs, tubers, and spores. However, there is a great 

 deal of variation among the various species of plants in the length 

 of the period of dormancy. In vi^•iparous plants, such as the man- 

 grove, the development of the embryo is continuous from the be- 



