1770 



A TEXTBOOK OF THEORETICAL BOTANY 



to be transferred from A.3 to S.3, from A. 2 to S.2 and from A.i to S.i 

 rather than a transference of pollen from anthers of one height to the style 



Fig. 1656. — Lythrum salicaria. Trimorphic flowers. For descrip- 

 tion see in text. 



of another. It will be seen that this is assisted by the fact that the styles 

 and anthers project sufficiently far out for the insect to alight directly on 

 them. 



This complex system of cross-pollination is termed trimorphism 

 and was originally investigated by Charles Darwin. As a result of a long 

 series of experiments he was able to show that the number of seeds produced 

 in the ovary was greatest when S.3 was pollinated by A.3, or alternatively 

 S.I by A.I. If S.2 or S.i is pollinated by A.3 the fertility of the seeds is 

 less and the same is true of any other similar cross. From this Darwin 

 proposed the term legitimate for the crossing of a style by pollen derived 

 from stamens of the same length, and illegitimate for crossings between 

 organs of different length. The offspring of illegitimate fertilization behave 

 as hybrids in so far as sterility is concerned. (See also p. 1279.) 



The Lythraceae include a number of tropical trees whose timber is of 

 economic value and we mav mention Physocalymma scaberrimum from 



