THE ANGIOSPERMAE 1507 



astonished the keepers by germinating after having been wetted during 

 the London " bhtz " in 1941. Becquerel tested old seeds stored in the 

 National Museum in Paris in 1900 and again in 1934. They were nearly 

 all seeds of Leguminosae and they showed life periods varying from 55 to 

 158 years. All these seeds are hard-coated and Becquerel attributed their 

 longevity to the very low moisture content (2 to 5 per cent.) and absence 

 of oxygen inside the testas. 



Experiments with buried seeds of common American weeds were begun 

 by Beal in Michigan in 1879. The seeds were mixed with sand in uncorked 

 bottles, which were buried neck downwards to keep out water. The first 

 germination test was in 1884, when eleven out of twenty-one species 

 germinated. At the test in 1940, after sixty years, only three species were 

 found to have survived: Oenothera biennis, Rumex crispus, and Verbascum 

 blattaria, but the last named still showed a 68 per cent, germination. It is 

 planned to extend the tests to a period of 160 years. 



Most of the species in these tests plainly fall into the mesobiotic class 

 and many of the commonly cultivated plants are also in this class. If curves 

 are drawn to show the drop in percentage germination against time, it is 

 seen that there is usually a fairly rapid loss of vitality in the first five years, 

 but the curves flatten out slowly and after fifteen to twenty years there 

 may be a few resistant seeds still alive in any batch. 



Microbiotic seeds are often intolerant of drying in the air. Seeds of 

 some Grasses, Oaks, Beech, Sugar-maple, Poplars and Willows, Citrus 

 species, and Hevea brasiliensis are all in this category. The seeds of many 

 alpine plants likewise have no obligate periods of dormancy and germinate 

 immediately after shedding, a feature which is reputed to be correlated 

 with the very short growing season they experience. This deduction is 

 somewhat weakened by the fact that the same character is shown by a 

 number of common weeds. 



Most of these seeds are not killed by drying as such, but apparently by 

 concomitant oxidations, since they can be dried even to exceptionally low 

 moisture contents, provided this is done at a low temperature, preferably 

 in the absence of oxygen. In this condition they will retain their vitality 

 for much longer than the normal periods, e.g., in Salix for nearly a year. 

 Possibly at higher temperatures bacterial growth may assist their deteri- 

 oration. 



Dispersal of Seeds. The dormancy of seeds makes them particularly 

 fit to be agents of dispersal as well as of reproduction. Every seed is a new 

 life and every seed w'hich is of biparental origin is a new whole, with new 

 potentialities. The survival of the species is best ensured by dispersing 

 the seeds to as many difl^erent localities as possible. In this way new geno- 

 types may find the conditions with which they best accord and develop 

 into new ecotypes. At the same time some degree of isolation will favour 

 their survival by lessening the chances of back-crossing with the parent 

 plant. Unrestricted competition between seedlings around the parent 

 plant would also greatly increase the mortality, with the loss of potentially 



