38 PRINCIPLES OF GARDENING. [CH. I. 



and I consider the most eligible mode of applying 

 the chlorine, was also suggested to me by the same 

 distinguished horticulturist. In this way he said he 

 made tropical seeds vegetate, which refused to ger- 

 minate by other modes of treatment. He placed 

 the mixed ingredients mentioned above in a glass 

 retort, inserting its bulb in the hot bed, and bringing 

 its beak mider the pot in which the seeds were so^mi 

 connecting it with the draining aperture of the pot. 

 The chlorine gas is gradually evolved, passing 

 through the earth of the pot to the seeds, with more 

 or less rapidity according to the heat employed. 



This absolute necessity for the presence of oxygen 

 is a reason why seeds will not germinate if buried 

 beyond a certain distance from the earth's surface ; 

 and why clayey soils often fail of having a good plant, 

 an impervious coat of the clay enveloping the seed, 

 and preventing the airs access. 



M. Bm'ger foimd that seeds of lye buried one inch 

 below the sui'face had their leaves above it in eight 

 days and a half, whereas those at a depth of sL\ inches, 

 had only just sprouted at the end of twenty-two days. 



But too deep sowing inflicts another injury ; though 

 it be not at such a depth as entirely to prevent ger- 

 mination, yet it so consumes the matter of the seed 

 in forming the useless elongation of stalk necessary 

 to bring the leaves above the surface, that all further 

 progress in vegetation has been prevented. M. 



