GERMINATION. 189 
at Toulouse, a young professor then, who excelled in inspiring his 
pupils with a taste for this sort of study. The wonderful inci- 
dents attending the nuptials of the Vallisneria spiralis, or still 
more the marvellous evolutions of the Nautilus floating on the 
sea, or disappearing in its depths at its own pleasure, were the 
favourite texts for the discourses of M. Joly during our botanical 
and geological excursions round Montpelier, in the flower-decked 
wood of La Valette, or on the volcanic summit of Monferier. 
Thirty years have elapsed since those happy youthful days, and 
the recollection is just as vivid, just as present to my mind as 
if I still heard the burning words of our then young teacher ring- 
ing in my ears, telling us, under our radiant skies, all about the 
wonders of nature, and the power of God. 
GERMINATION. 
In order that a seed should germinate, three conditions are 
requisite—heat, air, and moisture; temperature, varying in dif- 
ferent species, must not be much less than 10° or 15° (centigrade), 
and it must not reach higher than 40° or 45°. 
Moisture penetrating the seed beneath the ground softens it, 
swells all its parts, and allows their intimate evolution. : 
Air is also as indispensable to the germination of seeds as it is 
to animal life. Seeds which are buried too deeply in the ground, 
and are thus cut off from the air, will never germinate. 
What, then, is the important part that atmospheric air per- 
forms in the act of germination? It is just the same as that 
which it fulfils in the respiration of animals. Air acts on the 
seed by means of its oxygen. The germinating seed, like the 
animal, breathes out carbonic acid. It takes up carbon into its 
Own substance, and the carbon combines with the oxygen of 
the air to form carbonic acid; but from the instant when, by the 
progress of germination, the young plant has produced small green 
leaves, the chemical pkenomenon is, so to speak, reversed. In the 
daytime, and under the influence of light, the young plant absorbs 
carbonic acid from the air, and replaces it with oxygen ; its respi- _ 
ration takes place just as we stated when speaking of this physio- 
logical function in the green-coloured portion of vegetables. ) 
