164 APPLICATION OF PRINCIPLES. 



quired for germination ; and only to administer water 

 when the signs of germination have become visible ; 

 even then the supply should be extremely small. If 

 this is attended to, carbonic acid is very slowly form- 

 ed and liberated, the chemical quality of the contents 

 of the seed is thus insensibly altered, each act of respi- 

 ration may be said to invigorate it, and by degrees it 

 will be brought to a condition favourable to the assi- 

 milation of food in larger quantities. Mr. Knight 

 used to say that these effects were produced in no way 

 so well as by enclosing seeds between two pieces of 

 loamy turf, cut smooth, and applied to each other by 

 the underground sides ; such a method is, however, 

 scarcely applicable to ajiy except seeds of consider- 

 able size.* 



Other expedients have occasionally been had re- 

 course to successfully. Where seeds are enclosed in 

 a very hard dry shell, it is usually necessary to file it 

 thin, so as to permit the embryo to burst through its 

 integuments when it has begun to swell. Under natu- 

 ral circumstances, indeed, no such operation is prac- 

 tised: but it is to be remembered that such seeds will 

 have fallen to the ground as soon as ripe, and before 

 their shell acquired the bony hardness that we find 

 after having become dry. 



Sometimes it has been found useful to immerse 



* The sowing of very small and delicate seeds in the open air 

 should be deferred until the season is so far advanced, that all pro- 

 bable danger from cold weather is past. Suspending a shingle or 

 board over the place where they are sown, by laying it upon bricks 

 placed edgewise, until the first leaves are perfectly formed, will be 

 found a great advantage in sowing all delicate seeds. A. J. D. 



