AND INSECT AID. 233 



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." 



A long series of experiments proved that both kinds of pollen 

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

 and that no ovary is fully fertilisable in any other manner than by 

 stamens of the corresponding length. Nescea vcrticil/ata, a 

 common Lythraceous plant of the Atlantic United States, is, 

 according to Dr. Asa Gray, similarly trimorphous. Several South 

 African and American species of Oxalis are trimorphous, and 

 have been investigated by Darwin and Hildebrand, with the same 

 result as in Lyt/ini/n saliairia. Referring to trimorphism, Mr. 

 Darwin observes in one of his valuable works, as follows : — 

 " Fritz Miiller 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." " All known flowers," 

 writes Dr. Asa Gray, " exhibiting reciprocal dimorphism, or tri- 

 morphism, are entomophilous " (insect fertilisable). No such wind- 

 fertilisable species is known. Few of them are irregular, and 

 none very irregular ; they do not occur, for instance, in Legninin- 

 oSiC, Labiata:, Scrophulariaccn, OrcJiidacece, etc. Nature is not 

 prodigal, and does not endow with needless adaptations flowers 

 which are otherwise provided for. 



The last, but not the least remarkable example of the adapta- 

 tion of flowers to the visits of insects for the purpose of fertilisa- 

 tion to which I will allude is that of the Orchidaceous family of 

 plants. The flower of the Orchis is very abnormal. Its genera 

 vary amazingly in the structure of the anther, the column, the lip^ 

 and indeed of all parts, but in the consolidation of the style and 

 stamen they are all agreed. " The flowers," to quote the words 

 of an eminent modern botanist. Otto W. Thome, " are rarely 

 solitary, usually in spikes, racemes, or panicles ; and the superior 

 perianth consists of two whorls, each of three leaves. Of these, 

 the inner whorl is always irregular, and often has a spurred lii) or 



