49Q SCIENCE PROGRESS 



power of the seed when placed under field conditions. Let 

 us now consider in some detail the procedure followed in 

 ascertaining the germinating power of seed : — 



(i) Germinating Bed. — Excepting in the case of some of the 

 larger seeds, they are placed, without previous soaking, directly 

 in the seed-bed, without being in contact with one another. 

 The seed-bed varies. In some cases strong folded blotting- 

 paper is used, in others porous clay dishes of varying thickness, 

 in others sand, and in yet others (especially cereals) ordinary 

 soil in flower-pots or saucers in a greenhouse. I shall not stop 

 to mention the practical details to be observed in keeping these 

 media pure. In this Station the same seed is tested in two or 

 more of these media and the average result taken, this being 

 further checked by the simultaneous germination of a " control " 

 seed of known germinating power. I have found this additional 

 precaution very useful in cases of dispute between buyer and 

 seller, and recommend it for general adoption. 



(2) Temperature. — Whatever the nature of the bed may be, it 

 is essential that its temperature should be under control and 

 should remain constant. In most cases the temperature recom- 

 mended is 20 C. Here our results have been more satisfactory 

 when the thermometer of the incubator was 24 C. Certain seeds 

 (Poa, Dactylis, Beta, etc.) are found to germinate better if they 

 are also exposed each day to a temperature of 30 C. for six hours, 

 in imitation of the diurnal rise of temperature in nature. 



(3) Moisture and Seed-bed. — The process of dehydration 

 through which a seed passes in ripening has its counterpart 

 when germination is taking place. A dry seed will not ger- 

 minate, no matter how favourable the other conditions may be. 

 If, on the other hand, a seed is left water-logged it will not 

 germinate, but in a few days die and rot away. The seed-beds 

 used in testing are of a porous nature, in contact by partial 

 immersion or otherwise with fresh water, so that the necessary 

 moisture reaches the seed, generally by capillarity. For most 

 seeds the amount of moisture so obtained is sufficient. This 

 holds true for the seed-bed, whether of porous clay, sand, 

 asbestos, or blotting-paper, and for most seeds. 



(4) Air. — Fresh air is usually provided for in the incubators 

 by ventilators. Seeds are particularly sensitive to injurious 

 chemical substances, whether in the seed-bed or in the gas often 

 used in heating the incubator. 



