Angewandte Botanik. 31^ 



more slowly in dry storage. Impermeable seeds become permeable 

 more rapidly in wet blotters than in dry storage. 



It i3 impossible to estimate even approximately in advance the 

 Proportion of the impermeable seeds in any given lot which will 

 germinate in any given length of time under ordinary germination 

 conditions. A widely variable proportion of the impermeable seeds 

 of alfalfa, crimson clover, and the larger seeded commercial species 

 included in this investigation produce seedlings promptly in the 

 soil under greenhouse conditions or in the open field in warm 

 weather. Only in exceptional cases is this true of the impermeable 

 seeds of the clovers, other than crimson clover. 



The use of aqueous extracts from soil has no effect, and alter- 

 nate wetting and drying of the seeds has but little effect on the 

 germination of impermeable seeds. Within ordinary limits neither 

 the depth of planting nor the firmness of the soil affects the ger- 

 mination of impermeable clover and alfalfa seeds under green- 

 house conditions. These factors may affect the stand secured by 

 preventing some of the seedlings from reaching the surface. 



Storing impermeable clover and alfalfa seeds at a temperature 

 of 50° C. for one day or at 45° for six months has little or na 

 effect upon their germinating capacity or permeability. In wet 

 blotters a temperature of 36° very slightly increases the softening 

 of impermeable seeds, but also kills some of the seeds. Freezing, 

 when wet. causes the subsequent germination of many impermeable 

 seeds, but may kill some seeds which had previously softened. 

 Any constant temperature from 1° C to 30° has little effect upon 

 the softening of impermeable clover seeds. Alternations of tempera- 

 ture have but little effect on the softening and germination of 

 impermeable clover and alfalfa seeds if none of the temperatures 

 used in the alternation is cooler than 20° C. Alternations of tempera- 

 ture cause the softening and germination of many impermeable 

 clover seeds when a temperature of 10° or cooler is used in 

 alternation with a temperature of 20° or warmer. The effect of such 

 an alternation is greatly increased by previously exposing the seeds 

 to germination conditions at a cool temperature (10° C. or cooler) 

 and is decreased by previously exposing the seeds to germination 

 conditions at a warm temperature (30°). 



Even under the most favorable conditions only a small pro- 

 portion of impermeable red-clover, alsike-clover, white-clover. and 

 white sweet-clover seeds produces seedlings promptly in the soil 

 when sowed in warm weather. 



Impermeable seeds of red clover, alsike clover, white clover^ 

 and white sweet clover will pass the winter in the soil in a freezing 

 climate without injury. At least 50 or 60 per cent of them may be 

 expected to germinate in the soil the following spring unless a 

 part of them germinate during warm weather in the winter. If this 

 occurs, the seedlings produced in the winter are liable to be killed 

 by subsequent freezing. 



A large proportion of impermeable alfalfa, crimson clover, okra, 

 and hairy-vetch seeds will germinate in the soil during the first 

 few months after planting. some of them early enough to be of 

 importance to the crop. Nearly all alfalfa and okra seeds, even if 

 they are impermeable in the fall, are killed when they pass the 

 winter in the soil or on the plants out of doors in a freezing climate. 

 A small Proportion of the impermeable alfalfa seeds survive with 

 their vitality uninjured. Some of the okra seeds remain impermeable 



