262 



PLANT PHYSIOLOGY AND ECOLOGY 



ordinarily pass through a resting period are often brought into 

 conditions where they germinate at once, and perish because of 

 unfavorable factors, or because competing species are too far 

 advanced. Spores and seeds capable of immediate germination 

 may likewise be scattered abroad at a time when conditions make 

 growth impossible. The direction of movement is often decisive 

 because the seed or spore is either carried into a habitat suffi- 

 ciently like that of the parent to secure establishment, or into 

 one so dissimilar that germination is impossible, or at least is not 



Fig. 105. Detail of a salt basin formation, showing the ecesis beneath 

 and about the parent plants of Corispermum. 



followed by growth and reproduction. The rapidity and dis- 

 tance of migration have little influence, except in the case of 

 conidia, gemmae, etc., with little resistance to dryness. The 

 amount of migration, i.e., the number of migrants, is of the great- 

 est importance, since it directly affects the chances that vigorous 

 seeds will be carried into places where ecesis is impossible. 



278. The factors in ecesis. Ecesis may take place in a habitat 

 covered with plants, or in one that is without a plant covering. 

 The first case is by far the most frequent. In it, the invaders 

 must not only adjust themselves to the general physical factors 



