THE IMPERMEABILITY OF SEEDS 63 



longevity of seeds under those conditions. The question 

 whether impermeable seeds will preserve their vitality longer 



in the soil seems to be as yet unanswered. Although, as The question 



quoted in this paper, Duvel has shown that in the case of permeable ' 



ordinary seeds the advantage lies with seeds dried in air, he preslrw" 



did not determine this point for the hard seeds that did not }^^" vitality 



1 ■ • 1 T-. r T-. longer in the 



germmate m his experiments, apparently, as Froressor Ewart soil than in 

 observes, because he did not employ methods that would fully * ^ *"^' 

 test their germinative capacity. Commenting on the results 

 of the extensive experiments of Duvel and Waldron to deter- 

 mine the length of time weed-seeds must be buried in order 

 to lose their vitality, Crocker points out that " vitality tests of 

 this kind, that neglect the effect of the seed-coats, are tests of 

 the condition of the seed-coats rather than tests of the real 

 vitality of the embryos themselves " {Botanical Gazette, October 

 1906). In this connection the testimony of Professor Pammel 

 of Iowa is significant. As concerning the seeds of a number of 

 weeds, he found that the percentage of seeds germinating was 

 lower and the dormant period longer if the seeds were kept 

 during the winter in paper packages than if they were placed 

 in sand and exposed to the climatic conditions of an ordinary 

 winter (Brit. Assoc, 1909, "Nature," Octdber 28, 1909). 



It is nevertheless evident from the Australian observations 

 that even the most resistant of seeds tend to lose their im- 

 permeability in the course of years when kept in dry air. With 

 the loss of this quality the seed is not necessarily deprived of 

 its power of retaining its vitality for a longer period, since 

 typically permeable seeds, as has been already remarked, may 

 preserve their germinative capacities for many years. It, how- 

 ever, is deprived of the power of prolonging its existence in the 

 soil ; and in consequence it either germinates or dies. How 

 long a seed with impermeable coverings could remain alive 

 when buried deeply in the soil, it would be extremely difficult 

 to determine with accuracy. But it is apparent from Professor 

 Ewart's own observations that under the conditions of undis- 

 turbed primeval forest i^ Australia they might lie buried in the 



