382 CROSS-FERTILISATION. CHAP. X. 



tilisation, with many parts in the latter slightly 

 modified for this special purpose.* 



As two objects in most respects opposed, namely, 

 cross-fertilisation and self-fertilisation, have in many 

 cases to be gained, we can understand the co-existence 

 in so many flowers of structures which appear at first 

 sight unnecessarily complex and of an opposed nature. 

 We can thus understand the great contrast in structure 

 between cleistogamic flowers, which are adapted exclu- 

 sively for self-fertilisation, and ordinary flowers on the 

 same plant, which are adapted so as to allow of at least 

 occasional cross-fertilisation.t The former are always 

 minute, completely closed, with their petals more or 

 less rudimentary and never brightly coloured ; they 

 never secrete nectar, never are odoriferous, have very 

 small anthers which produce only a few grains of pollen, 

 and their stigmas are but little developed. Bearing 

 in mind that some flowers are cross-fertilised by the 

 wind (called anemophilous by Delpino), and others 

 by insects (called entomophilous), we can further 

 understand, as was pointed out by me several years 

 ago,J the great contrast in appearance between these 

 two classes of flowers. Anemophilous flowers resemble 

 in many respects cleistogamic flowers, but differ widely 

 in not being closed, in producing an extraordinary 



* Nature,' 1873, pp. 44, 433. the old nest. The fully-deve- 



f Fritz Miiller has discovered loped males and females are 



in the animal kingdom ( ' Je- winged, and individuals from dis- 



naische Zeitschr.' B. iv. p. 451) tinct nests can hardly fail often 



a case curiously analogous to that to intercross. In the act of 



of the plants which bear oleis- swarming they are destroyed in 



togamic and perfect flowers. He almost infinite numbers by a host 



finds in the nests of Termites, in of enemies, so that a queen may 



Brazil, males and females with often fail to enter an old nest; 



imperfect wings, which do not and then the imperfectly deve- 



leave the nests and propagate the loped males and females propagate 



species in a cleistogamic manner, and keep up the stock, 

 but only if a fully-developed queen J 'Journal of Linn. Soc.' vol 



after swarming does not enter vii. Bot. 1863, p. 77. 



