286 DKECIOUS AND CHAP. VII. 



apparently quite destitute of pollen. Considering how 

 many Eubiaceous genera are heterostyled, it is a 

 reasonable suspicion that this Asperula is descended 

 from a heterostyled progenitor; but we should be 

 cautious on this head, for there is no improbability in 

 a homostyled Eubiaceous plant becoming dioecious. 

 Moreover, in an allied plant, Galium cruciatum, the fe- 

 male organs have been suppressed in most of the lower 

 flowers, whilst the upper ones remain hermaphrodite; 

 and here we have a modification of the sexual organs 

 without any connection with heterostylism. 



Mr. Thwaites informs me that in Ceylon various 

 Eubiaceous plants are heterostyled; but in the case of 

 Discospermum one of the two forms is always barren, 

 the ovar} r containing about two aborted ovules in each 

 loculus; whilst in the other form each loculus contains 

 several perfect ovules; so that the species appears to 

 be strictly dioecious. 



Most of the species of the South American genus 

 ^Egiphila, a member of the Yerbenaceae, apparently are 

 heterostyled; and both Fritz Miiller and myself thought 

 that this was this the case with JE. obdurata, so closely 

 did its flowers resemble those of the heterostyled species. 

 But on examining the flowers, the anthers of the long- 

 styled form were found to be entirely destitute of pol- 

 len and less than half the size of those in the other form, 

 the pistil being perfectly developed. On the other hand, 

 in the short-styled form the stigmas are reduced to half 

 their proper length, having also an abnormal appear- 

 ance ; whilst the stamens are perfect. This plant there- 

 fore is dioecious; and we may, I think, conclude that 

 a short-styled progenitor, bearing long stamens exserted 

 beyond the corolla, has been converted into the male; 

 and a long-styled progenitor with fully developed stig- 

 mas into the female. 



