EVOLUTION OF PLANTS AND THE DIRECTIVITY OF LIFE. 555 



obvious, but with or without any intermediate condition of secreting 

 honey as in the Pasque-flower. 



If the petals be observed from the middle of the flower of a Water- 

 lily to the circumference, the anthers will be found to get smaller 

 till they quite disappear, and a perfect petal results, composed solely 

 out of a broadened filament. 



We must now consider the uses of the floral organs. 



Everyone now knows that no seed can be " set " or give rise 

 to a new plant unless the pollen has reached the stigma of the carpel 

 which contains the ovule, which must be fertilized by the pollen. 

 All flowers are so constructed that this can be secured either by " self- 

 pollination," when the pollen from the anthers is applied to the 

 stigmas in the same flower ; or the flower may be " crossed " by 

 pollen carried by the wind from one flower to another ; or, lastly, 

 it may be conveyed by insects or, rarely, by birds. One notices that 

 flowers solely fertilized by pollen brought by the wind are not attractive 

 by means of colours or scents ; as in most grasses, docks, sedges, and 

 some trees, as the hazel, oak, and poplar. 



Those which are habitually self-fertilized are for the most part 

 insignificant little flowers, often scarcely, if at all, expanding ; and a 

 noticeable feature about them is that such plants are by far the most 

 prolific ; and, though often small herbs and annuals, will soon smother 

 other plants, as in a neglected garden ; as, e.g., groundsel, shepherd's 

 purse, Solanum nigrum, &c. Flowers conspicuous by being white or 

 coloured, with or without scent, are constructed so as to attract insects, 

 which in visiting one flower get dusted with pollen often in a definite 

 part of the body. This part is then struck by the stigma of another 

 flower of the same kind, the stigma of which is purposely so situated 

 as to receive the pollen conveyed to it. 



It was the innumerable ways in which this " crossing " is secured 

 that led Darwin to say "Nature abhors self-fertilization." He 

 subsequently withdrew this strong statement ; for his experiments 

 showed him that when a plant was artificially self-pollinated, and 

 the results compared with others of the same kind which had been 

 artificially crossed, not infrequently the offspring of self-pollination 

 beat those of his crossed plants both in height and fertility ! 



The question at once arises, how did " irregular " flowers arise 

 from the others ? In a regular flower the members of the " whorls " 

 are all alike, as those of the calyx, corolla, stamens, and carpels 

 respectively in Buttercups ; whereas, in the Labiates, the petals 

 (united into a tube) are not exactly alike, the front petal being 

 enlarged to form a lip, just as in Orchids &c. Indeed, in Salvias, 

 the departures from " regularity " are about twenty in number, 

 every one of which is a useful, purposeful adaptation, primarily 

 for the benefit of the insect ; so that it in return will most easily 

 pollinate the stigma with greater certainty. 



It will be observed in all flowers habitually crossed, that the honey- 

 secreting gland is just where the tongue or proboscis of the insect is 



