ECESIS 55 



extremely diverse, though, as would be expected, it is much 

 longer as a rule for seeds than for spores. The greater 

 vitality of seeds in the case of ruderal plants suggests that 

 this diversity may be due simply to variation in the vigor of 

 the embryos. It would seem that under proper conditions 

 seeds may retain their viability for an indefinite period. 



The influence of habitat upon germination is of primary 

 importance, though the manner in which its influence is ex- 

 erted is by no means as evident as might be supposed. In 

 the case of seeds sown in the planthouse, it is almost uni- 

 versally the case that germination is less than in nature, 

 notwithstanding the fact that temperature and moisture 

 appear to be optimum. In nature, the seeds of the species 

 may be carried into a number of different formations, any 

 one or all of which may present conditions unfavorable to 

 germination. With respect to probability of germination, 

 habitats are of two sorts, those which are denuded and those 

 which bear vegetation. It is impossible to lay down general 

 propositions with respect to either group, since germination 

 will vary with the character of the invading species, the 

 annual distribution of heat and moisture in the habitat, etc. 

 In a general way, however, it maybe stated that the chances 

 for germination are greater in vegetation than in denuded 

 areas, chiefly because the latter are usually xerophytic. On 

 the other hand, the lack of competition in the denuded area 

 tends to make ultimate establishment much more certain. 

 Here, as elsewhere whan exact statistical results are desired, 

 the use of the quadrat, and especially of the permanent 

 quadrat, is necessary to determine the comparative germina- 

 tion of the invading species in relation to denudation and 

 vegetation. 



The seedling once established by germination, the prob- 

 abiUty of its growing and maturing will depend upon its 

 habitat form, plasticity and vegetation-form. Even though 

 it may germinate under opposite conditions, a typical hylo- 

 phyte, such as Impatiens for example, will not thrive in an 

 open meadow, nor will characteristic poophytes, such as 

 most grasses, grow in deep shade. In the same way, 



