PEErACE TO THE EEPEINT OF 1884 IX 



gynodiceciousness. Three different forms occur, but on 

 any given plant the flowers are of one kind. There is 

 a normal hermaphrodite form, and two divergent forms 

 which are practically male and female, and which are 

 distinguished from the hermaphrodite form by ha,ving 

 conspicuous sexless ray-florets ; of the two, the male 

 flowers are the more conspicuous. The female florets 

 have shrunken anthers devoid of pollen ; the male florets 

 have pistils which do not open, and are therefore 

 functionless. Numerous gradational forms exist 

 which render the whole case especially instructive, and 

 it was a study of these gradations which induced Muller 

 to give up his theory of gynodicecious plants. 

 Muller formerly explained the origin of gynodicecious- 

 ness by supposing that those flowers which are smaller 

 and less conspicuous than the average tend to be visited 

 last by insects, so that their pollen is useless. In 

 Centaurea the reduction of anthers is found beginning 

 in flower-heads which are noi less conspicuous than 

 the average. Muller therefore gives up his former 

 theory and agrees with view proposed by my father.* 



Potonie ('Sitz. d. Ges. naturforsch. Freunde zu 

 Berlin,' 1880, p. 85, quoted in the 'Bot. Zeitung,' 

 1880, p. 749) believes that in the gynodicecious Salvia 

 pratensis the existence of a female form serves to ensure 

 fertilisation by a distinct plant. 



But H. Muller (' Bot. Zeitung,' 1880, p. 749) shows 

 that in the hermaphrodites, bees commonly visit the 

 lower and temporarily female flowers before passing on 

 to the upper male flowers, and that this ensures 

 cross-fertilisation between different plants. 



Solms-Laubach ('Abhand. K Gesell. Wiss. G-ot- 

 tingen, xxviii., and Kosmos,' 1881) has given in his 



* A short paper by H. Muller on gynodioeoiousuess in the geims 

 Dianthus, appeared ia_' Nature,' 1881i xxiv. ' 



