THE ORIGIN OF PETALS. 



centre of most ordinary blossoms. The simplest 

 type of flower consists of two such organs only, a 

 pistil or ovary containing an embryo seed, and a 

 stamen which produces the pollen necessary to im- 

 pregnate it. The production of seed is in fact the 

 sole function of the flower ; every additional part is 

 only useful in so far as it conduces to this practical 

 end. In the most simple (though not the most 

 primitive) blossoms, fertilisation is effected by a grain 

 of pollen from a stamen falling upon the stigma or 

 sensitive surface of the pistil, and thence sending 

 forth a pollen-tube, which penetrates the ovule or 

 embryo seed, and so impregnates it. 



As a rule, however, it is not desirable that a flower 

 should be fertilised by pollen from its own stamens. 

 Mr. Darwin has shown in many cases that when a 

 pistil is fecundated by pollen from a neighbouring 

 blossom, or still better from a different plant, it sets 

 more and sounder seeds, or produces heartier and 

 stronger young seedlings. To attain the benefits of 

 such cross-fertilisation, many plants have acquired 

 special peculiarities of structure : or, to put it more 

 correctly, those plants which have spontaneously 

 varied in certain favourable directions have been 

 oftenest cross-fertilised, and have thus on the average 

 produced more and stouter offspring. The advantage 

 thus gained in the struggle for existence has enabled 

 them to live down their less adapted compeers, and 

 to hand on their own useful peculiarities to a large 

 number of descendants. There are two ways in 

 which plants have ensured such a benefit ; the one is 

 by adapting themselves to fertilisation by means of 

 the wind, the other is by adapting themselves to 



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