344 
the influence of the pollen, and at the time of fertilization exudes a viscous 
fluid. 
Most flowering plants have the stamens and pistils in the same flower, and 
are said to be perfect or hermaphrodite; others, as the hazel, melon, and corn, 
have the stamens and pistils in different flowers on the same plant; others, 
again, as hemp and the hop, have male flowers on one plant and female flowers 
on another. In some species, these three kinds of flowers are found on the 
same plant. 
The conditions required for the germination of seeds are moisture, heat and 
access to air. Light appears to be injurious; darkness may therefore be con¬ 
sidered necessary also. Seeds absorb a large quantity of w T ater; the office of 
water, in the first place, is to soften the nutritive matters of the seed. The 
amount of heat required to excite the vitality of the seeds of different species 
of plants, varies considerably. Seeds of tropical plants require a high tempera¬ 
ture to induce them to germinate. Air, or rather the oxygen of the air, is es¬ 
sential to germination. If seeds are buried deep, they do not vegetate. Some 
kinds retain their vitality for years when buried deep in the soil; hence it is no 
uncommon occurrence, when land has been subsoil-ploughed or deep-drained, 
for species of plants to appear, differing from those which had been observed 
in the same locality previously. 
Seeds have been made to vegetate in a certain quantity of air by Saus- 
sure and others, who, by determining the composition of the air before 
and after germination, proved that germinating seeds absorb oxygen and 
give off' carbonic acid. This gas is formed by oxygen combining with a 
portion of the carbon contained in the seed. By this chemical action heat 
is produced, and the comparatively insoluble starch of the seed is con¬ 
verted into soluble gum or sugar, upon which the embryo can feed. The 
process of converting barley into malt affords a familiar illustration of the 
ehemicial changes induced by germination. When a seed begins to germi¬ 
nate, the radicle or primary root of the embryo first lengthens; in what¬ 
ever position a seed may be placed the radicle invariably avoids the light 
and descends into the soil, and the plumule to which light is essential, as 
certainly ascends through the soil to the light. During germination a 
certain degree of heat and moisture and access to air, are the conditions 
required; when the cotyledons appear above ground, carbonic acid and 
light are essential to the further progress of the young plant. 
