Chapter II. 



GERMINATION. 



INFLtTENCE OF UNIFORM TEMPERATURE ON GERMINATION OF 



SEED. 



The results of his own experiments on the germination of seeds at 

 different temperatures were published by De Candolle (1865). His 

 object was to determine the effect of long exposures at low tempera- 

 tures as compared with short exposures at high temperatures. He 

 eliminated various sources of complication and extended the observa- 

 tions made by Burckhardt (1858). Great pains were taken to. keep 

 the seeds at a uniform temperature; the water with which they 

 were wetted was previously brought to the temperature required by 

 the experiment. The first wetting was quite copious. The seeds 

 were first covered with a thin layer of sand and the wettings fre- 

 quently washed them bare, but no difference was observable in the 

 epoch of germination for naked and covered seeds, showing that the 

 temperatures in the inclosures were very uniform. The thermometers 

 were carefully reduced to a standard Centigrade and their readings 

 are probably correct within a tenth of a degree. The moment of 

 germination is a delicate point to fix and is somewhat arbitrary. 

 The embryo changes within the seed before any change shows itself 

 on the outside. De Candolle takes as the moment of germination that 

 when, the spermoderm being broken, the radicle begins to issue 

 forth. Burckhardt in his experiments took as the epoch of germina- 

 tion the moment when the cotyledons show themselves; but in De 

 Candolle's opinion this is rather an epoch of vegetation than the 

 epoch of germination. It would perhaps be well to consider this 

 phenomenon when we compare the same species under different con- 

 ditions; but it varies very much from one species to another, since 

 certain plants remain for a long time recurved under the earth or 

 with their cotyledons imprisoned in the remnants of the spermoderm. 



The seeds experimented on were as follows : 



Crucif erae Lepidium sativum . 



Do Sinapis alba. 



Do Iberis amara. 



Polemoniaceae Collomia coccinea. 



Linaceae Linum usitatissimum. 



Cucnrbitaceae Melon ( cantaloupe) . 



RanuncTilaceae Nigella sativa. 



Pedalinefe Sesamum orientate. 



Legiiminoseae Trifolium repens. 



Gramine;e Zea mays, var. precoce. 



Amarantaceae Celosia cristata. 



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