164 Agricultural Section [PT u 



so much of the pure seed. The presence of seeds of other culti- 

 vated plants may or may not reduce the value of a sample, but 

 the presence of weed seeds, especially of noxious kinds, is always 

 objectionable. The presence of even small proportions by weight 

 of weed seed should not be ignored, because the actual number 

 represented may be enormous. The following list taken at 

 random will make this clear. 



The presence of one per cent. Represents approx. 



by weight of : per Ib. 



Yorkshire Fog (Holcus lanatus, L.) (in glumes) ... 9,000 seeds 



,, (without glumes) ... 13,000 ,, 



Ox-eye Daisy (Chrysanthemum leucanthemum, L.) ... 11,000 



Chickweed (Stellaria media, Cyrill.) 12,000 



Mouse- ear Chickweed (Cerastium vulgatum, L.) ... 35,000 



Docks (Eumex sp.) 3,000 



Sheep's Sorrel (Rumex acetosella, L.) 10,000 



Creeping Buttercup (Ranunculus repens, L.) ... ... 3,000 



Slender Foxtail (Alopecurus agrestis, L.) 2,500 



Wavy Hair-grass (A ira flexuosa, L.) 8,000 



Tussock Grass (Aira csespitosa, L.) 25,000 



This short list will serve to show that only one per cent, of 

 weed seed in a sample may produce serious results for the pur- 

 chaser. For example, if we assume that a mixture of grass seeds 

 contains the above weeds in equal proportions, but not exceeding one 

 per cent, by weight of the entire bulk, then each pound of the mixture 

 will contain about 12,000 weed seeds. Since something like 

 30 pounds of grass seed per acre is usually sown for permanent 

 pasture it follows that such a mixture would introduce some 

 360,000 weed seeds to the same area, i.e. nearly 80 to each square 

 yard. 



A reference to Chap, vm will show what are the usual im- 

 purities to look for in any kind of seed, and also what percentage 

 of pure seed may be reasonably expected in each case. By means 

 of the illustrations of weed impurities given on pages 137, 144-146, 

 149, 156 and 158, and by reference to the descriptions of grass seeds 

 given in Chaps, vi and vn, most of the harmful impurities may be 

 identified. 



3. Germination. Even when a sample is reasonably pure 

 the vitality of the seed may for various reasons be low. For 

 instance, the seed may be imperfectly or irregularly matured, it 



