50 PASTURES AND PASTURE PLANTS CHAP. 



Impurities. — All sand, chaff, stones, earth, seeds of other species or 

 varieties, and broken or badly damaged seeds of the kind being tested must 

 be regarded as impurities. 



Method of Procedure. — The "smaller average sample" should be 

 spread out on a smooth, black or white surface, such as an enamelled board, 

 while the impurities are carefully separated out and weighed ; so that the 

 percentage of pure or true seeds may be easily calculated. 



Identification of Weeds. — So far as possible each weed-seed must be 

 identified, because some are very much more noxious than others. 



The presence of certain species is sometimes useful in determining the 

 nationality of the seed under investigation ; but too much reliance must not 

 be placed on conclusions of this description, owing to the ubiquitous nature 

 of most weeds, and also to the fact that seeds of various nationalities are often 

 rriixed into one bulk. 



Testing for Germination 



Essentials for Tests. — The absolute essentials for accurate tests are 

 suitable temperature, proper supply of moisture and free ventilation, though 

 darkness is also highly desirable. 



Temperature of Tests. — The normal temperature of germination under 

 natural conditions is from 55° — 65° F. ; and in artificial tests a constant tem- 

 perature between 60° and 80° F. should be maintained. The heat of an 

 ordinary living-room will, however, generally be found sufificient for home-tests, 

 though a little fire may be advantageously provided if the night-temperature 

 appear likely to fall very low. 



Supply of Moisture. — Free access to water is necessary, but seeds do not 

 germinate satisfactorily when immersed ; so that some such medium as felt, 

 flannel, stout blotting-paper, etc., must be employed to supply abundant 

 moisture without permitting water to actually accumulate round the seeds. 



Ventilation of Tests. — Free access of air is most important, as carbonic 

 acid gas is given off by the germinating seeds. 



Darkness of Tests. — Light appears to exert a directly harmful influence 

 on germination, so all tests should, as far as possible, be made in darkness, 

 excepting those of seeds of the Meadow-Grasses (Poas), which do not germinate 

 in darkness, but »msi be tested in the light. Yellow oat-grass seeds also 

 germinate better in the light than in darkness. 



Selection of Seeds. — Some of the genuine or pure seeds separated in 

 the purity test are employed in the germination trials ; and it is most essential 

 that those used should fairly represent the sample, proper proportions being 

 taken of large, small and medium-sized, light and dark-coloured grains, of 

 different stages of maturity. 



Selecting Grass Seeds. — In the case of some grass seeds, it is not an 

 easy matter to at once distinguish between empty glumes and those containing 

 grains ; but this difificulty is surmounted by wetting the seeds and spreading 

 them on a sheet of glass, which must be held up to the light, when the useful 

 seed will appear opaque, and the chaff or empty glumes, translucent. 



Number of Seeds. — As it is always desirable to make duplicate trials, 

 two lots of 200 seeds of each leguminous species and three lots of 200 se.eds 

 of any grass should be tested. 



Preparing Seeds. — Since seeds soon become mouldy in a warm, moist 

 atmosphere, it is well to hasten the process of germination by soaking them 

 in water for from 6 to 1 5 hours before placing them in the germinator. 



