436 



A NGIOSPERMAEDICOTYLEDONES 



1034. L. Salicaria L. (Charles Darwin, ' On the Sexual Relations of the three 

 Forms of Lythrum Salicaria/ J. Linn. Soc. Bot., London, viii, 1865, pp. 169-96, 

 ' Different Forms of Flowers ' ; Herm. Muller, ' Fertilisation/ pp. 255-60.) Charles 

 Darwin investigated the flower mechanism of this species in an extremely thorough 

 manner, and proved by numerous experiments that the ' reproductive organs, when of 

 different length, behave to one another like different species of the same genus 

 in regard both to direct productiveness and the character of the offspring ; and that 

 consequently mutual barrenness, which was once thought conclusive proof of 

 difference of species is worthless as such, and the last barrier that was raised 

 between species and varieties is broken down' (Herm. Muller, op. cit., p. 258). 



Before considering Darwin's experiments in detail, a description of the flower 

 mechanism will be given. 





Fig. 148. Scheme of the legitimate unions possible in Lythrum (after Charles Darwin). A. Long- 

 styled form. B. Medium-styled form. C. Short-styled form. The dotted lines indicate the anthers 

 from which pollen must pass to the stigma of each of the three forms, so as to give a legitimate union 

 with complete fertility. 





Hermann Muller says that the nectar is secreted by the fleshy base of the 

 receptacle, surrounding the short stalk of the ovary, and filling the space between 

 this and the receptacular wall. The red inner surface of the calyx, and the dark 

 veins of the petals (which converge to the middle of the flower), serve as nectar- 

 guides. The flowers are horizontal, usually hexamerous (more rarely pentamerous), 

 and not strictly actinomorphous. The petals are inserted into the edge of the 

 cylindrical receptacle (5-7 mm. long), and the three lower petals are usually some- 

 what longer than the upper ones, which are 6-10 mm. in length. When the flower 



