40 
POPULAR SCIENCE REVIEW. 
and so produce that degree of crossing which is beneficial. 
It has been found that the size and colour of the corollas of 
flowers (as in the geraniums), the intensity of their per- 
fumes, or the (more practical) larger amount of honey which may 
be secreted in their nectaries, are always proportioned to the 
needs of the flowers to be crossed by pollen other than their own. 
So necessary is this crossing in some instances that the pistil of 
a flower is as barren when dusted with pollen from its own 
stamens as if it had been fertilized with pollen from an 
altogether different species. It had long been acknowledged 
in a general way that flowers were necessary to insects ; but 
it is only within the last few years that it has been discovered 
that insects are quite as necessary to flowers. With the 
exception of accidental crossing, which may result from 
such fringe-winged insects as the minute little Thrifts to 
be seen in most English flowers, the insects which can 
fertilize or cross different flowers, so as to make their visits 
important and serviceable, are limited to two or three orders. 
Of the orders of insects now recognized by zoologists, one may 
be regarded as specially adapted to flowers. This is the order 
Lepidoptera, a peculiarly flower-haunting group all over the world, 
both in the day-flying species called butterflies, and the night- 
flying species known as moths. Their mouths are in the shape 
of a trunk or proboscis, which does not allow them to suck food 
except in a fluid state, such as that in which we find the 
natural honey of plants. To this universal fact of the Lepidop- 
tera being purely suctorial, there is only one exception in the 
case of the curious moths in Australia ( Ofthideres ), which 
have boring or terebrant mouths ; thus linking the Lepidoptera 
with other orders of insects. Next to the Lepidoptera in 
importance to flowers as an order, are the Hymenoptera, of 
which, however, only the bees are purely flower-frequenters ; 
a good many members of this order being even disadvantageous 
to flowers. Among them we may instance the numerous species 
of ants, whose fondness for the honey secreted by flowers in- 
duces them to climb the stems of plants for the purpose of obtain- 
ing it. But as these insects are wingless (except a particular 
set at a certain time of the year, when flowers have nearly all 
bloomed), and as their bodies are glossy and bare of the hairy 
covering which in butterflies, moths, and bees enables the pollen 
to stick to the body, it follows that ants cannot be serviceable to 
flowers in crossing them ; whilst if they steal the honey offered 
as a reward to serviceable insects, they are so far actually enemies. 
It is to protect flowers against such predatory excursions as those 
made by vigilant ants that their stems are covered with hairs 
and prickles, or gummy with viscid secretions. Some of the 
Coleoptera or beetles, such as the rose-chafers, and various 
