[53] I lay stress here on the _practical_ signification of "Species."
Whether a physiological test between species exist or not, it is hardly
ever applicable by the practical naturalist.
[54] The humble bees, on the other hand, are direct helpers of some
plants, such as the heartsease and red clover, which are fertilized by
the visits of the bees; and they are indirect helpers of the numerous
insects which are more or less completely supported by the heartsease
and red clover.