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to demonstrate the effect of electricity on vegetation, objected 
to the conclusions of these philosophers, and affirmed that the 
difference in the germination of seeds in the shade and in the light 
was owing, not to the light itself, but to the difference in the 
moisture in the two situations ; the moisture evaporating much 
faster from the seeds in the light than from those in the shade ; 
and he affirmed, that when precautions were taken to keep the 
seeds equally moist, those in the sun germinated sooner than 
those in the shade. But when Mr. Sennebier repeated his for- 
mer experiments, and employed every possible precaution to 
ensure equality of moisture in both situations, he constantly 
found the seeds in the shade germinate sooner than those in the 
light. We may conclude, therefore, that light is injurious to 
germination ; and hence one reason for covering seeds with the 
soil in which they are to grow. But from the recent experiments 
of Saussure, there is reason to believe that light is only injurious 
in consequence of the heat which it produces ; for when the 
direct rays of the sun were intercepted, though light was ad- 
mitted, the germination of the seeds was not sensibly retarded. 
Thus we have seen that seeds will not germinate unless mois- 
ture, heat, and oxygen be present. Now, in what manner do 
these substances affect the seed ? AVhat are the changes which 
they produce ? It was observed before, that all seeds have one 
or more cotyledons. These cotyledons contain a quantity of 
farinaceous matter, laid up on purpose to supply the embryo 
plant with food as soon as it begins to require it. This food, 
however, must undergo some previous preparation before it can 
be applied by the plant to the formation or completion of its 
organs. It is probable that all the phenomena of germination 
which we can perceive, consist in the chemical changes which 
are produced in that food, and the consequent development of 
the organs of the plant. 
When a seed is placed in favourable circumstances, it gradu- 
ally imbibes moisture, and very soon after emits a quantity of 
carbonic acid gas, even though no oxygen gas be present. If 
no oxygen gas be present, the process stops here, and no ger- 
mination takes place ; but if oxygen gas be present, a portion 
of it is converted into carbonic acid gas. From the experi- 
ments of Saussure, it appears, that if seeds be left to germinate 
in a determinate portion of oxygen gas or common air, the bulk 
