106 . TYPES OF BRITISH PLANTS 
no need to take trouble in order to attract insects. The 
most interesting plants are certainly those which have 
not only the double machinery for producing seeds, but 
also prefer that the two machines shall come from 
different individuals. To bring pollen from a neighbour- 
ing plant two agencies are employed, first the wind, and 
second insects, which call on a plant for honey, get dusted 
with ripe pollen, and then go off to another flower and 
touch the stigma. As we go through the various types 
of British flowering plants, we shall meet with all sorts 
of devices to secure this end, to the pursuit of which we 
owe the bright hues of our prettiest flowers, and not only ~ 
their colour, but their scent and their sweet honey. We 
shall also find excellent examples of the distribution by 
wind when we consider the Pines and Firs, and the 
Grasses. 
Before leaving this part of the subject I would like 
to mention two very strange instances of collaboration 
of plants and insects for their mutual advantage, which 
are as curious as the lichen partnerships of alge and 
fungi discussed earlier. They may very well be men- 
tioned at this point, for both plants are foreigners, and 
we should not meet them again in the study of our 
English families. The first is the case of the Yucca 
plant and a moth that frequents it; the second that of 
the Fig tree and a kind of gall-wasp. 
The Yucca is a plant that you may have seen in 
Botanical Gardens, bearing a tall spike of greenish-white 
flowers (or occasionally of another hue, according to 
specific variation). These flowers are specially attractive 
to a night-flying moth called Pronuba, and in their turn 
they depend upon it to be fertilised. They therefore 
reverse the usual process of plant-life, and their bell- 
