POSITIVH DEDOUBLEMJKNT. 85 



stamens, viz., the two posterior lateral ones, most of 

 the other genera having at least four stamens. Flowers 

 of Veronica occur abnormally with three, four, or five 

 stamens : an interesting case of reversion. 



The majority of the Oleace^ have only two stamens, 

 which may be either the two lateral, as in the lilao 

 {Sijringa), or the two median ones (Jasminum), of the 

 ancestral tetrandrous flower ; this last is to-day re- 

 presented by Tessarandr(f, which has four stamens. 

 Buchenau observed a flower of Syringa in 'which the 

 two lateral stamens were replaced by two small petals, 

 and the two median stamens of the ancestor had 

 reappeared ; this latter phenomenon being probably 

 the cause of the former, or vice-versa. 



In most species of willow {Salix) the number of 

 stamens is two; many observers have noted the 

 presence in abnormal flowers of three, four, or five 

 stamens ; clearly a reversion to a condition which is 

 the normal feature in other species, such as S. triandra 

 and S.pentandra, which represent, in their andrcBcium, 

 older types than the more common diandrous form. 

 The poplar (Popiduti) must be regarded as a still older 

 type in which polyandry obtains. 



The normal flower of Crucifer^ has an outer whorl 

 of two lateral stamens and an inner whorl of four, 

 approximated in pairs in the median plane. According 

 to the law of reduction, which we are now coming to 

 perceive is of very wide-spread jjrevalence in the 

 vegetable kingdom, the Cruciferous flower is really 

 a much later reduced condition of that of the closely- 

 allied order Capparidacea), in typical forms of which 

 the flower is polyandi^ous. Celakovsky has elaborated 

 the whole matter admirably, and the reader is referred 

 to his treatise on this and other orders for what is 

 probably the best and most thorough-going account 

 of floral evolution. Abnormal flowers of the wall- 

 flower (Glu'iranthus Gheiri) have been seen with eight 

 stamens, four in the outer whorl instead of the usual 

 two (fig. 96 a). This is, on the theory of reduction, a 



