CHAP. Ill MITCHELLA REPEXS. 125 



RUBIACE.E. 



This great natural family contains a much larger 

 number of heterostyled genera than any other one, as 

 yet known. 



Mitclidla repens. Prof. Asa Gray sent me several 

 living plants collected when out of flower, and nearly 

 half of these proved long-styled, and the other half 

 short-styled. The white flowers, which are fragrant 

 and which secrete plenty of nectar, always grow in 

 pairs with their ovaries united, so that the two together 

 produce "a berry-like double drupe."* In my first 

 series of experiments (1864) I did not suppose that 

 this curious arrangement of the flowers would have any 

 influence on their fertility ; and in several instances 

 only one of the two flowers in a pair was fertilised ; 

 dnd a large proportion or all of these failed to produce 

 berries. In the ensuing year both flowers of each 

 pair were invariably fertilised in the same manner ; 

 and the latter experiments alone serve to show the 

 proportion of flowers which yield berries, when legiti- 

 mately and illegitimately fertilised; but for calcu- 

 lating the average number of seeds per berry I have 

 used those produced during both seasons. 



In the long-styled flowers the stigma projects just 

 above the bearded throat of the corolla, and the 

 anthers are seated some way down the tube. In the 

 short-styled flowers these organs occupy reversed posi- 

 tions. In this latter form the fresh pollen-grains are 

 a little larger and more opaque than those of the long- 

 styled form. The results of my experiments are given 

 in the following table. 



* A. Gray, 'Manual of tic Bot. of the N. United States,' 185G, 

 p. 17*. 



