GERMINATION CAPACITY 621 



avoided if good results are to be expected. Some seeds, how- 

 ever, maintain their power of growth several years without 

 deterioration. 



The time during which seeds will maintain their power of 

 germination, in an unimpaired condition, depends upon many 

 circumstances, storage and ripeness in particular. There is 

 much diversity of opinion upon this point, and the experiments 

 recorded vary considerably in their results on account of the 

 almost certain want of uniformity of quality of seed to begin 

 with in the different series of experiments. 



For practical purposes, however, the following table, compiled 

 from various sources, indicates the time beyond which it is in- 

 advisable to use the seeds mentioned : 



Formerly useful species of Brassica, as turnips and swedes, 

 were much adulterated with dead seed of charlock and useless 

 weed seeds of similar size and colour. Care was taken to kill 

 the weed seeds by exposure to heat, in order that the fraud might 

 not be detected by the appearance of wrong kinds of plants in 

 the field. 



At the present time old seed is frequently mixed with new, 

 and is a cause of the weak and poor quality of many samples 

 met with in commerce. 



Poor germinating capacity may also be due to imperfect 

 development of the embryo during ripening, mechanical injury 



