POLLEN-CARRYING 



they are always designed to fulfil a perfectly definite pur- 

 pose, and that all their details are contrived accordingly. 



This purpose is to carry the pollen from the stamens of 

 one flower to the stigma of another. The pollen can usually 

 be recognized as a yellowish or reddish dust formed in the 

 stamens ; this dust is generally rubbed off" on an insect's 

 proboscis or on part of its body. When the insect reaches 

 another flower the pollen is scraped off* by a sticky or 

 gummy stigmatic surface. When the pollen has been placed 

 on this surface it grows, germinates, and part of it unites 

 with the egg-cell of the young seed. 



The latter is then, and not till then, able to become ripe 

 and mature. It may be compared to cross-breeding in 

 animals, though the process does not exactly correspond. 



But all flowers do not require insects to carry their pollen. 

 In early geological periods we do not find any flowers like 

 those that now exist, nor in those early times were there 

 any flies, bees, or butterflies. 



The cockroach seems to have existed in Silurian (whin- 

 stone) times, and many gigantic and extraordinary insects 

 lived in those damp forests of ferns, club-moss, and horsetails, 

 of which the remains now form our British coalfields. May- 

 flies, plantbugs, and especially dragonflies (some of them 

 with wings two feet across) existed, but none of these insects 

 are of much use as pollen-carriers. 



Even much later on, when screw pines, monkey-puzzle trees, 

 ginkgos, and bamboos formed the forests and woods of 

 Europe, crickets and earwigs existed ; but it is not until that 

 geological period in which the chalk was formed (the Creta- 

 ceous age) that fossil plants like most of those now familiar 

 to us occur. These had flowers intended for insects, and 

 with the fossil plants we find the fossils of the insects that 



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