Aug. 14, 1916 Agricultural Value of Impermeable Seeds 783 



and sweet-clover seeds which were impermeable increased under dry- 

 storage in the laboratory. Nearly all of the seeds which softened after 

 wintering in the soil or on the plants germinated. 1 



2. Only those alfalfa seeds which remained impermeable survived the 

 winter on the plants. Only 3 per cent of those seeds gathered in the 

 spring germinated and 97 per cent were impermeable. Of those gathered 

 in the fall 76 per cent germinated and 22 per cent were impermeable, only 

 2 per cent being dead. 



Additional tests were made upon self-sowed seed in February and 

 March, 191 6, taking advantage of the effect of a favorable alternation of 

 temperatures upon the softening of the seeds (see p. 779-781), as follows: 



One lot of self-sowed red-clover seed and two lots of self -sowed sweet- 

 clover seed, with the soil in which they were embedded, were gathered on 

 February 29 and immediately placed in an ice box in which the tempera- 

 ture was constantly somewhat below io° C. During the next few days 

 the seeds were separated from the soil without allowing them to become 

 dry at any time. Both before and after removing them from the soil they 

 were daily alternated between the ice box and the germinating chamber 

 at 30 . 



Many seeds had produced seedlings, and others had softened but had not 

 germinated in the field. Many of the seed which were impermeable when 

 taken into the laboratory softened in the next four days. After the 

 fourth day there was very little change during the following three weeks, 

 although the seeds were incubated in the ice box for nine days and then 

 again alternated between the ice box and the chamber at 30 C. 



The numbers of seeds and seedlings recovered from the soil were as 

 follows: Of red clover, 4,610; of the two lots of sweet clover, 1,508 and 

 and 980, respectively. By the end of the fourth day after collecting the 

 seeds, 86, 54, and 66 per cent of these different lots had softened either in 

 the field or in the laboratory. If it be assumed that 90 per cent of these 

 seeds were impermeable the preceding fall, it can be calculated that 84, 

 49, and 62 per cent of the impermeable seeds softened. 



Besides the leguminous seeds already considered, eight lots of okra 

 seeds were gathered in April, 1913, after passing the winter in the field. 

 The great majority of these seeds were dead, but the percentage of dead 

 seeds varied according to the previous exposure, being 69 per cent of the 

 seeds in closed pods on the ground, 91 per cent of the seeds in closed 

 pods on the stalks, 95 per cent of the seeds in opened pods on the stalks, 

 99 per cent of the seeds in opened pods on the ground, and all of the 

 shelled seeds lying looc2 on the ground. Of the seeds which softened 

 without clipping none germinated except of those which had been win- 

 tered in closed pods on the ground, where they had the full protection 



1 In this connection Hume's observations on sweet clover in South Dakota are interesting (12). Unhulled 

 sweet-clover seed was sowed in August, 1911 and in 1912. Only a few seedlings were produced the year the 

 seeds were sowed, but in each case a good stand of sweet-clover plants came up the following spring. 



