GERM1XATION REQUISITES FOR IT. 293 



and 113 F. as the highest they can bear in sand or earth. Wheat, 

 Oats, and Barley, are said to thrive in any country where the mean 

 temperature exceeds 65 F. The spores of certain cryptogamic plants 

 are especially fitted for cold countries. Edwards and Colin found that 

 seeds in a dry air bore a higher temperature than in water or steam. 



611. Air, or rather oxygen, was shown by Scheele to be necessary 

 for germination. Seeds deeply buried in the soil, and excluded from 

 air, do not spring. The depth at which seeds should be sown, varies 

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

 The following experiments were made by Petri : 



Seed sown to the Came above ground No. of plants that 

 depth of in came up. 

 inch 11 days 7-8ths. 



1 12 all. 



2 .18 7-8ths. 



3 20 6-8ths. 



4 21 4-8ths. 



5 22 3-8ths. 



6 23 l-8th. 



Shallow sowing is thus proved to be the best. 



612. 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 subsoil 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 

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

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

 same thing is observed after the burning of forests, and the draining 

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

 to the trees which spring up after the burning of the virgin forests 

 (matos virgens and capoes), 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 micrantha sprung up ; and seeds gathered from under six 

 feet of peat-moss in Stirlingshire have been known to germinate. Mr. 

 Kemp mentions the germination of seeds found at the bottom of a 

 sand-pit 25 feet deep, which he concludes from various circumstances, 

 to have been deposited more than 2000 years ago. The seeds were 

 farinaceous, belonging to the natural order Polygonacese. A weak 

 solution of chlorine is said to accelerate germination, probably by the 

 decomposition of water, and the liberation of oxygen. 



613. Darkness is favourable to germination. Seeds germinate best 

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



