at Different Degrees of Constant Temperature. 245 
evening of the 16th of March, some of the seeds germinated on 
the 27th in the evening, 7. e. the eleventh day, and others con- 
tinued to sprout successively. It is difficult to determine to what 
this difference of from eleven to seventeen days was owing ; for 
the surrounding temperature was 0° in both cases. I suspected 
that the seeds in the second sowing were not brought sufficiently 
near 0° at the moment at which they were placed in the soil, which 
was of this temperature. They were also but few in number, 
and too crowded. It may be that the outer temperature had not 
surrounded them with sufficient rapidity at first, and that, a 
certain chemical change having ensued, the approximation of 
the seeds had produced a local heat sufficient to alter the supposed 
conditions. For these reasons, the result of the first experiment 
(seventeen days) appears to me to be most probably correct. 
At the end of thirty-five days, being obliged to absent myself, 
I ceased to renew the ice in the apparatus; but the experiment 
had lasted sufficiently long. And what proves it, was, that at 
my return nearly a month later, on the 9th of May, I found the 
vessels in the apparatus at 7°°7, and no other species except the 
Sinapis had germinated. Several might have sprouted at simi- 
lar temperatures, as we shall see presently ; but in such a pro- 
longed experiment they had probably rotted. Lepidium and 
linseed germinate at ordinary temperatures, almost as soon as 
Sinapis, and would certainly have germinated between the seven- 
teenth and the thirty-fifth day of the experiment if the tempera- 
ture of O° had not formed an obstacle. 
There are probably alpine species which sprout below a tem- 
perature of 0°, especially nival species, as So/danella for example. 
We are advised to sow the seeds of rhododendrons in melting 
snow, and foresters sometimes sow in the same way the seeds of 
trees on mountain-slopes. Undoubtedly, in the natural course 
of things, the rays of the sun between whiles may cause a rise of 
temperature above 0° at the expense of the water of the snow; 
but we may believe that, as in the instance of Stnapis, certain 
species germinate whenever water comes into contact with them, 
even at 0°. On the other hand, according to my experiments, 
several do not germinate at so low a temperature. It still 
remains to be determined whether they really cannot germinate, 
or whether they require so long a time that their tissue usually 
passes into a state of putrefaction which reaches the embryo. 
Temperature of 1°:4: to 2°2. 
Four small porous earthen vessels were immersed up to the 
rim in the sawdust surrounding the reservoir of ice. On the 
7th of March, at 4 p.m., the seeds of all the above species, ex- 
cept the melon and Trifolium repens, were placed in them. The 
