ECESIS. 69 



from which further migration is possible, and so on. The time of year in 

 which fruits ripen and migration occurs has a marked influence upon the 

 establishment of a species. Migrules ordinarily pass through a resting-period, 

 but are frequeiltly brought into conditions where they germinate at once and 

 then perish, because of unfavorable conditions, or because of competition. 

 The direction and distance of movement are decisive in so far as they deter- 

 mine the kind of habitat into which the seed is carried. The number of mi- 

 grants is likewise important, since it affects the chances that seeds will be 

 carried into bare areas where ecesis is possible. 



In the case of algae, migration and ecesis become nearly or quite synony- 

 mous, since plants of this sort are at home almost anywhere in the water. 

 Indeed, it may be said that they are always at home, because they remain 

 in the same habitat, no matter where carried. With aquatic flowering plants 

 the case is somewhat different. The plants when free behave much as algae 

 do in regard to ecesis, but each new individual has to go through the processes 

 of germination and growth. This is similar to what occurs in the aggregation 

 of land plants. The seeds or imderground buds do not find themselves in a 

 new home exactly, but, apart from the greater certainty of success, the course 

 of ecesis is the same. 



The term ecesis, from the Greek olxijais, the act of coming to be at home; 

 hence, adjustment to the habitat, or oIkos, was first proposed (Clements, 

 1904: 32) to designate the whole process covered more or less completely by 

 acclimatization, naturalization, acconunodation, etc. It has proved so definite 

 and convenient in use that it seems desirable to employ a corresponding verb, 

 edze, from oi/clfw, to make a home, colonize. 



Germination. — ^The first critical process in ecesis is germination. The exact 

 scope of germination is debatable, but in nature it is most convenient to regard 

 it as including the appearance and unfolding of the first leaf or leaves, whether 

 cotyledons or not. It occurs regularly when a viable seed meets favorable 

 conditions as to water, heat, and oxygen. It is often delayed or even absent 

 when the seeds of native species are first sown under mltivation, and it is 

 probable that germination is often delayed in nature, even when conditions 

 seem favorable. A viable seed must contain a normal embryo, capable of 

 absorbing water, and using the stored food for growth and consequent escape 

 from the seed-coats. The amount of water, heat, and oxygen present must 

 suffice to bring the seedling to the point where it can make food and begin its 

 own independent existence. Hysterophytes are naturally exceptions. 



With the exception of seeds of forest trees and certain ruderals, we have 

 practically no accurate knowledge of the germinability of natiye species, 

 especially at those times when conditions favor germination. The normal 

 period of viability under the usual conditions of natural sowing is also unknown, 

 as well as viability under extremely favorable and imfavorable conditions. 

 In most cases the period of duration is a function of the seed-coats or pericarp, 

 but in some viability is inherent in the embryo itself. The control of the 

 habitat is two-fold. It determines whether the seed will germinate either 

 immediately or during the season. If germination is delayed, it determines 

 whether conditions wiU permit the seed to remain dormant but Adable- for 

 several years. Habitats which are most favorable to germination are least 

 favorable to dormant seeds, and, conversely, those which allow seeds to persist 



