1278 



A TEXTBOOK OF THEORETICAL BOTANY 



A B 



Fig. 1214. — Annelid maritima. A and B, The two respective types of 

 stigma, each carrying the opposite type of pollen. In the centre, 

 A-type pollen below, B-type pollen above. {After Iversen.) 



and are cross-pollinated. The shorter ones lie among the anthers and are 

 directly self-pollinated. Smaller flowers may have all four styles short and 

 self-pollinated. Several species in Ranunculaceae and Rosaceae have hetero- 

 stylous hermaphrodite flowers and produce male flowers with abortive 

 carpels. The classic case of higher complexity is, however, that of hetero- 

 tristyly or heterostylous trimorphic flowers, best known in Lythriim sali- 

 caria, the Purple Loosestrife (Fig. 1215), but also found in several other 

 genera. Here again Charles Darwin gave the first account of the mechanism 

 of pollination. There are three kinds of flowers: first, the long-styled, with 

 six mid-length and six very short stamens and the style projecting consider- 

 ably beyond all of them. Secondly, the mid-styled flower, which has six very 

 short stamens, six which are as long as the style in the first type of flower, and 

 a style which is mid-length. The third flower is short-styled and has six mid- 

 length and six long stamens, while the style is only as long as the short stamens 

 in the other flowers. The long style is more than three times as long as the 

 shortest one, and the stigmas and anthers are also graduated in size according 

 to the development of the respective styles and stamens. A striking peculiarity 

 is that the short and mid-length stamens have yellow pollen, but the longest 



