o_o a. a 
Fertilization of Flowering Plants. 189 
honey from rain, and so lead to its being hidden in tubes and 
spurs, and only accessible to the visits of particular insects. The 
lines and markings we find on many corollas all serve as guiding 
marks to the honey, and they are absent from flowers which open 
at night. Sprengel, in 1798, was the first to show how much 
plants are dependent on the visits of insects, and to point out 
that the forms and colours of flowers are adapted to ensure and 
profit by those visits. To give an instance, many years ago red 
clover was introduced into Australia, and for some time did not 
produce any seed, the humble-bee, which was in the habit of 
visiting the flowers, not having been introduced with it; but 
since this insect has become naturalized the red clover flourishes 
and produces seed in abundance. 
The legs of bees are admirably adapted for collecting pollen by 
means of the brush-like tufts of hair that cover them. The 
proboscis is also long, and can be inserted into tubular flowers. 
There are many contrivances exhibited by flowers to keep away 
unwelcome visitors, such as the wingless forms of insects, which 
cannot readily pass to other flowers; among these are viscid 
glandular hairs, as in species of Dianthus, Silene, and Plumbago ; 
or tufts of hair, as in the periwinkle and cow-wheat ; or extreme 
smoothness of surface, as in many orchids; or the mouth of the 
flower is contracted or even closed, as in the antirrhinum. 
Flowers in most cases are accessible to winged insects only, and 
it is only when a large number of small flowers are grouped 
together in close proximity that creeping insects find a welcome. 
But it will be said that insects visit all kinds of flowers, and 
will therefore take the pollen from one flower and deposit it on 
another of a different species. So indeed they do, and when the 
species are nearly related hybrids are produced ; but insects visit 
flowers of the same species as long as they can, as was observed 
by Aristotle with respect to the hive-bee more than 2000 years 
ago. Darwin suggests that the cause of this is that they are 
probably able to work more quickly, that they have just learned 
how to stand in the best position on the flower, and how far and 
in what direction to insert their probosces. One point must be 
noticed, that bees are sometimes so anxious to save time that 
they bite a hole through the base of the corolla to save them- 
selves the trouble of inserting their probosces into the opening ; 
but, as Darwin points out, it is chiefly flowers growing in crowded 
situations that are thus perforated (short-tongued bees). 
One of the most frequent methods of securing cross-fertilization 
is when the stamens and pistils attain their functional activity at 
different times; the stamens in some cases and the pistils in 
others. The flowers of Arwm and Aristolochia are examples of 
the latter, and both are visited by flies and midges. The insects 
push by fringes of hairs pointing downwards, and thus give easy 
c 
