346 GERMINATION — REQUISITES FOR IT. 



from half-an-incli to two inches, according to the nature of the soil. 

 The following experiments were made by Petri : — 



Shallow sowing is thus proved to be the best. 



Seeds, when buried deep in the soil, sometimes lie dormant for 

 a long time, and only germinate when the air is admitted by the 

 process of subsoU ploughing, or other agricultural operations. When 

 ground is turned up for the first time it is common to see a crop of 

 white clover and other plants spring up, which had not been pre- 

 viously seen in the locality. After the great fire in London, plants 

 sprang up, the seeds of which must have long lain dormant ; and the 

 same thiog is observed after the burning of forests and the draining 

 of marshes. Gardner says that the name capoeira is given in Brazil 

 to th'e trees which spring up after the burning of the virgin forests 

 (matos virffens), and that they are always very distinct from those 

 which constituted the original vegetation. Mr. Vernon Harcourt 

 mentions a case where turnip seeds lay in a dormant state for seven 

 or eight years, in consequence of being carried down to a great depth 

 in the soil. On the Calton Hill, at Edinburgh, when new soil was 

 turned up some years ago for building, a large crop of Fumaria mic- 

 rantha sprang up ; and seeds gathered from under six feet of peat- 

 moss in Stirlingshire have been known to germinate. A weak solution 

 of chlorine is said to accelerate germination, probably by the decom- 

 position of water, and the liberation of oxygen. Weak solutions of 

 chlorate of potash, of nitric acid, and of oxalic acid, are also said to 

 accelerate the sprouting of seeds. 



Darkness is favourable to germination. Seeds germinate best 

 when excluded from light. M. Boitard showed this by experiments 

 on Auricula seeds, some of which were covered by a transparent bell- 

 jar, others by a jar of ground glass, and a third set by a jar enveloped 

 in black cloth. The last germinated most rapidly. Senebier con- 

 cluded that the height and size of a plant were proportionate to the 

 intensity of the illumination, its verdure dependent on the quality of 

 the rays. Mr. Hunt says that the luminous or light-giving rays, and 

 those nearest the yellow, have a marked effect in impeding germina^- 

 tion; the red or heat-giving rays are favourable to the process, if 

 abundance of water is present ; while the blue rays, or those concerned 



