61 



in Eastern North America and frequently cultivated. 

 Flowers, purplish, petals six to seven. Spiked Loosestrife 

 is classic because of Darwin's work in connection with 

 heterotristylous flowers. Darwin proved beyond a question 

 that the reproductive bodies, when of difl'erent lengths, behave 

 like different species of plants, that is to sav, the pollen taken 

 from a short stamen and placed upon the long style in the 

 same flower or plant has no effect. So, too, of all the other 

 stamens taken from the same plant. Darwin also demon- 

 strated that the pollen grains differ 

 as well as the stigmatic papillae.' 

 The pollen grains of the longer 

 stament are green, those from the 



PIG. 25. 

 Fig. 2.5. Lythrum aalicaria. 1, long styled flower from above, with two sets of 

 stameus ; part of calyx and corolla removed ; 2, mid-styled flower ; 3. short-styled 

 flower; a, long anthers and stigmas; ft. mid-styled; c, short; d, honey gland; 

 /, mid-styled flower viewed obliquely. (After Hermann Mueller). 



middle size and the shoitest are yellow. The pollen grains 

 also vary in size. The longest stamens have the largest pol- 

 len grains and the shortest, the smallest. 



In this plant three kinds of flowers are produced. One 

 j)lant produces only a short style with long stamens and 

 mid-styled stamens; a second plant has a long style with 



