ADAPTATIONS FOR INTERCROSSING. 239 



independent proof that pollen is carried on the proboscis ; for a 

 small branch of a protected short-styled plant (which produced 

 spontaneously only two capsules) was accidentally left during 

 several days pressing against the net, and bees were seen insert- 

 ing their proboscides through the meshes, and in consequence 

 numerous capsules were formed on this one small branch. . . . 

 It must not, however, be supposed that the bees do not get more 

 or less dusted all over with the several kinds of pollen ; for this 

 could be seen to occur with the green pollen from the longest 

 stamens. . . . Hence insects, and chiefly bees, act both as 

 general carriers of pollen, and as special carriers of the right 

 sort." 



429. Finally, a long series of experiments (requiring eighteen 

 distinct kinds of union) proved that both kinds of pollen are 

 nearly or quite impotent upon the stigma of the same flower, and 

 that no ovary is fully fertilizable by other than a " legitimate 

 union," i. e. by stamens of the corresponding length ; but that 

 the mid-length pistil is more prolific than either of the others 

 under illegitimate union of either kind ; which might perhaps be 

 expected, as the pollen proper to it is intermediate in size of 

 grains between that of the long and that of the shortest stamens. 



430. Nesaea verticillata, a common Lythraceous plant of the 

 Atlantic United States, is similarly trimorphous, but has not 

 yet been particularly investigated. Several South African and 

 American species of Oxalis are equally trimorphous, and have 

 been investigated by Darwin and Hildebrand, 1 with results 

 quite as decisive as in Lythrum Salicaria. One genus of 

 Monocot}'ledons has trimorphous blossoms, viz. Pontederia, of 

 which the North American P. cordata is a good illustration. 2 



431. All known flowers exhibiting reciprocal dimorphism or 

 trimorphism are entomophilons : no such wind-fertilized species 

 is known. Few of them are irregular, and none very irregular : 

 they do not occur, for instance, in Leguminosse, Labiatae, 



1 Monatsber. Akad. Berlin, 1866 ; Bot. Zeit. 1871, &c. According to 

 Darwin, Fritz Mueller "has seen in Brazil a large field, many acres in extent, 

 covered with the red blossoms of one form [of an Oxalis] alone, and these 

 did not produce a single seed. His own land is covered with the short-styled 

 form of another species, and this is equally sterile ; but, when the three 

 forms were planted near together in his garden, they seeded freely." Forms 

 of Flowers, 180. 



2 Detected by W. H. Leggett. See Bulletin of Torrey Bot. Club, vi. 62, 

 170; and for the original discovery in Brazilian species, by Fritz Mueller, 

 see Darwin's Forms of Flowers, 183, &c. Pontederia has three lengths of 

 style and counterpart stamens, as in Lythrum Salicaria, each flower having 

 two sets of stamens, three in each set. 



