218 THE STRUCTURE OF FLOWERS. 



apparently truly heterostyled, but from Mr. Darwin's obser- 

 vations he thinks the shoi't-styled incapable of fertilisation ; 

 moreover the anthers of the long-styled form were " brown, 

 tough, and devoid of pollen." He considers that, from having 

 been heterostyled, it has now become dioecious, or else gyno- 

 dioecious. 



M. W. Burck has shown* that several genera of 

 RubiaceoB are heterostyled in form but quite dioecious. 



Faramea affords another curious difference. In the long- 

 styled form the stigma is short and broad ; in the short- 

 styled, it is long, thin, and curled. The anthers of the 

 short-styled are a little larger than those of the long-styled, 

 and the size of their pollen grains are as 100 : 67. But the most 

 remarkable difference (of which no other instance is known) 

 is in the fact that while the pollen grains of the short-styled 

 forms are covered with sharp points, the smaller ones are 

 quite smooth. The anthers, moreover, rotate outwards in 

 the short-styled, but do not do so in the long-styled flowers. 

 A similar rotation takes place in some of the Cruciferce, and 

 facilitates intercrossinof. A somewhat analogous torsion 

 occurs in some styles and stigmas, as of Linum perenne, 

 Luzula arvensis, Begonia, etc. 



The smaller and smooth pollen, in the more degenerate 

 condition of the long-styled form, is suggestive of the origin 

 of that of wind-fertilised flowers, which has sometimes 

 acquired the same form. Indeed, the two forms of pollen 

 (figured by Mr. Darwin at p. 129 of Forms of Floivers) exactly 

 correspond to the very common spinescent form in inter- 

 crossing species of Comj^osite, and to that of the anemophilous 

 Artemisia of the same order, respectively. 



The general conclusion, therefore, derived from the com- 



* 8ur V Organisation Florale chez quelques Rubiac^es. Ann. Jard. 

 Bot. Buitenzorg 3, p. 105. 



