Chapter II. 
GERMINATION. 
INFLUENCE 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: 
Cruciteras= Lepidium sativum. 
1 Be Nearest See tue Sinapis alba. 
1B oye. teghetae eee Tberis amara. 
Polemoniacez . ----- Collomia coccinea. 
MAnaCeO ee se Linum usitatissimum. 
Cucurbitaceze ------ Melon (cantaloupe). 
Ranunculacee - ---- Nigella sativa. 
iRedalines ses === Sesamum orientale. 
Leguminosee ------ Trifolium repens. 
Gramine® --------- Zea mays, Var. precoce. 
Amarantaceee ------ Celosia cristata. 
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