296 CAUSES OF DEGENERATIVE EVOLUTION 



It is to be noticed, however, that the variability 

 of vestiges is frequently considerable. The flowers 

 of Asparagus officinalis are sometimes, although 

 rarely, hermaphrodite. Usually they are uni- 

 sexual and exhibit the organs of the other sex in 

 every conceivable stage of degeneration. It is 

 probable that the unisexual condition has been 

 acquired recently, and that there has not yet been 

 time for the operation of natural selection to cause 

 the disappearance of the useless organs. 1 



1 We have actual knowledge of the mode of disappearance of an 

 organ in one case, and can see the part played by variability. In 

 Phyllanthus speciosus (Xylophylla arbuscula) the adult plant has 

 three kinds of branches : vertical branches, with rudimentary 

 leaves ; oblique branches which spring from the axils of these 

 leaves and themselves bear in two rows very rudimentary leaves ; 

 and flat branches which are the chief organs of assimilation of the 

 plant and which also bear rudimentary leaves in two rows. In the 

 seedling, on the other hand, there are formed after the two coty- 

 ledons, one or two completely developed assimilating leaves upon 

 an upright stem (fig. 84, A). 



The flat branches grow from the axils of these, and bear, 

 unlike the flat branches of the adult, assimilating leaves ; higher 

 up the vertical stem bears only rudimentary leaves with flat 

 branches in their axils. 



It may happen, however, that the seedlings bear, directly after 

 their cotyledons, rudimentary leaves (fig. 84, B) and in this case 

 the reduction of the leaves is present not only in the leaves borne 

 upon the vertical stem but in those borne on the flat branches. 

 These latter bear only a small number of assimilating leaves. 

 Thus, we have in this plant a remarkable example of incomplete 

 recapitulation : the seedling preserves in a functional condition 

 organs that are rudimentary in the adult, but the species furnishes 

 instances where these leaves cease to be functional even in the 



