A NATURALIST IN BRAZIL 



is always possible that the pollen may fall from the stamens directly 

 on to the stigma of the same flower, since this is surrounded by the 

 stamens. As a matter of fact, we find many such instances of self- 

 fertilization, but in the majority of cases the plants have tried to 

 avoid this method; as a rule by ensuring that the male and female 

 organs of a flower become ripe at different times, so that when the 

 pollen is ripe the stigma is not yet ready to receive it, but opens 

 only when the stamens of the same flower are withered. But self- 

 fertilization may be made impossible by the positions of the male 

 and female organs. We can understand why the plants endeavour 

 to guard against self-fertilization; for this is the highest imaginable 

 degree of inbreeding, exceeding even the marriage of brother and 

 sister, and examples in the lives of human beings and domestic 

 animals have taught us how quickly inbreeding may be productive 

 of bad results. 



It is therefore to the advantage of the plants if the pollen from 

 the flower of one plant is conveyed to the stigma of the flower of 

 another plant. In the case of many trees, such as the Conifers, the 

 Hazels and the Birches, and also in that of the grasses, the pollen 

 is blown off* by the wind and carried far across country. Ponds 

 are sometimes covered with the yellow dust; persons whose 

 mucous membranes are peculiarly susceptible become afflicted 

 with hay fever ; and when the air is so full of pollen it is natural 

 that a grain will sometimes fall on the stigma of a plant of the 

 same species. 



Most of the pollen, however, is lost, so that the plants had to seek 

 some means of getting the precious dust carried directly from flower 

 to flower. Such vehicles were found in the insects, which were able 

 to fly through the air, and were small enough to alight upon a flower 

 without breaking it or pulling it off". 



But for their services as go-betweens in this matter of fertilization 

 the plants had to offer them some reward, for otherwise why should 

 the insects ever visit the flowers? The plants therefore began to 

 secrete a sweet, nutritious substance in their flowers — flower-honey, 

 or nectar, as it is better to call it, for we give the name of honey to 

 the nectar after it has been elaborated by the bee. Now, the plants 

 had to call the attention of the insects to this nectar, and so they 

 developed, round their blooms, bright petals, which could be seen 

 from a distance, and from the midst of these petals they sent forth 

 a perfume which filled the surrounding air. In this way an increas- 

 ingly intimate and friendly relation between the insects and the 

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