146 NATURAL FERTILISATION 



" Cleistogamous" or self-fertilising Flowers. 



The most singular, however, of these special contrivances 

 for self-fertilisation are the peculiarly-shaped " cleistogamous " 

 flowers, as they have been termed which occur in many 

 plants belonging to widely-separated natural orders, either 

 intermixed with the ordinary conspicuous flowers or appearing 

 at a different time of the year with respect to which very 

 little has been written in English botanical works. Among 

 the natural orders in which these flowers have been found are 

 Violaceae, Cistaceae, Oxalideae, Balsamineae, Polygalaceae, Cary- 

 ophyllaceae, Malpighiaceae, Leguminosae, Campanulaceae, Con- 

 volvulaceae, Acanthaceae, Labiatae, and one order of Endogens, 

 Commelynaceae. The two species of Impatiens or Touch- 

 me-not which grow wild in this country /. Noli-me-tangere, 

 native in Westmoreland and some other rocky and woody 

 parts, and / fulva, a North American plant fully naturalised 

 by the banks of the Wey and other parts of Surrey, as well as 

 the smaller 7. parviflora, now also rapidly becoming com- 

 pletely naturalised in the neighbourhood of London have 

 closed, imperfect, self-fertilised flowers intermixed with the 

 showy yellow ones. They are far more numerous than the 

 conspicuous flowers, much smaller, and easily recognised even 

 in the bud. The calyx is quite regular, not presenting the 

 " spur " of the open flowers, always remains perfectly closed, 

 and is pushed off at the extremity of the seed-vessel in the 

 form of a little brown cap. The petals are entirely absent. 

 The stamens are of an altogether different shape to those of 

 the larger flowers, and contain but a very small quantity of 

 pollen, which, however, is amply sufficient for the fertilisation 

 of the ovules, the full number of seeds appearing to be always 

 produced. The most easily observed instances are, however, 

 in the case of our common wild Violets, the Sweet Violet 

 ( Viola odorata), or the various forms of the Dog Violet ( V. 

 canina). The existence of these flowers in Viola was known 

 as long ago as the time of Linnaeus, who, in his ' Praelectiones 

 Botanicae,' says that the flowers of Viola mirabilis produced 

 in the spring are often barren ; while the later ones, which 

 have no corolla, are fertile. Von Mohl has seen the pollen 

 escape from the anthers on to the stigmas, and give out 

 abundance of pollen-tubes. Monnier says that the ordinary 

 spring flowers of Viola hirta and V. odorata never produce 

 seed ; but this statement is disputed by others. The 

 cleistogamous flowers of the Violet appear long after those 



