147 
Seeds, although supplied with moisture and placed in a pro- 
per temperature, will not germinate, provided atmospherical air 
be completely excluded from them. Mr. Ray found that grains 
of lettuce did not germinate in the vacuum of an air pump, 
but they began to grow as soon as air was admitted 1o them. 
Homberg made a number of experiments on the same subject, 
which were published in the 3Iemoirs of the French Academy 
for the year 1693. He found that the greater number of seeds 
which he tried refused to vegetate in the vacuum of an air pump. 
Some, however, did germinate : but Boyle, Muschenbroek, and 
Boerhave, who made experiments on the same subject in suc- 
cession, proved beyond a doubt that no ])lant vegetates in the vac- 
uum of an air pumj) ; and that in those cases in which Romberg’s 
seeds germinated the vacuum was far from perfect, a quantity of 
air still remaining in the receiver. It follows, therefore, that no 
seed will germinate unless atmospherical air, or some air having 
the same properties, have access to it. It is for this reason that 
seeds will not germinate at a certain depth below the surface of 
the earth. 3Ir. Scheele found that beans would not germinate 
except oxygen gas were present : Mr. Achard afterwards proved 
that oxygen gas is absolutely necessary for the germination of 
all seeds, and that no seed w ill germinate in azotic gas, or hy- 
drogen gas, or carbonic acid gas, unless these gasses contain a 
mixture of oxygen gas. These experiments have been con- 
firmed by Mr. Gough, 3Ir. Cruikshank, and many other phi- 
losophers. It follows, therefore, that it is not the whole atmos- 
pheric air, but merely the oxygen gas which it contains, that is 
necessary for the germination of seeds. Nay, Mr. Humboldt 
has ascertained that seeds vegetate more rapidly when steeped 
in chlorine, or when watered with it ; and this substance is well 
known for the facility with which it decomposes water and sets 
at liberty oxygen. It seems even to augment the vegetative 
power of seeds. At Vienna several seeds which had been long 
kept, and which had constantly refused to germinate, grew rea- 
dily when treated with it. 
Light also has considerable influence on the germination of 
seed. Ingenhousz found that seeds always germinate faster in 
the dark than when exposed to the light. His experiments were 
repeated by Mr. Sennebier with equal success. But the Abbe 
Bertholin, who distinguished himself so much by his labours, 
174 ADCTABICM. 
