292 BOTANY [CHAP. X 



II. MELASTOMACE^:, 1862 1881. 



The following series of letters (pp. 293-302) refers to the Melasto- 

 maceas and certain other flowers of analogous form. In 1862 Darwin 

 attempted to explain the existence of two very different sets of stamens 

 in these plants as a case of dimorphism, somewhat analogous to the state 

 of things in Primula. In this view he was probably wrong, but this 

 does not diminish the interest of the crossing experiments described in 

 the letters. The persistence of his interest in this part of the subject is 

 shown in the following passage from his Preface to the English transla- 

 tion of H. Miiller's Befruchtung der Blumen ; the passage is dated Feb., 

 1882, but was not published until the following year. 



" There exist also some few plants the flowers of which include two 

 sets of stamens, differing in the shape of the anthers and in the colour 

 of the pollen ; and at present no one knows whether this difference 

 has any functional significance, and this is a point which ought to be 

 determined." 



It is not obvious why he spoke of the problem as if no light had been 

 thrown on it, since in 1881 Fritz Miiller had privately (see Letter 629) 

 offered an explanation J which Darwin was strongly inclined to accept. 

 Fritz Miiller's theory with regard to the Melastomads and a number 

 of analogous cases in other genera are discussed in H. Miiller's article 

 in Kosmos? where the literature is given. F. Miiller's theory is that 

 in Heeria the yellow anthers serve merely as a means of attracting 

 pollen-collecting bees, while the longer stamens with purple or crimson 

 anthers supply pollen for fertilising purposes. If Miiller is right the 

 pollen from the yellow anthers would not normally reach the stigma. 

 The increased vigour observed in the seedlings from the yellow anthers 

 would seem to resemble the good effect of a cross between different 



1 H. Miiller published (Nature^ Aug. 4th, 1881) a letter from his 

 brother Fritz giving the theory in question for Heeria. Todd (American 

 Naturalist, April 1882), described a similar state of things in Solanum 

 rostratum and in Cassia : and H. O. Forbes (Nature, Aug. 1882, p. 386) 

 has done the same for Melastoma. In Rhexia virginica Mr. W. H. 

 Leggett (Bulletin Torrey Bot. Club, New York, VIII., 1881, p. 102) 

 describes the curious structure of the anther, which consists of two 

 inflated portions and a tubular part connecting the two. By pressing 

 with a blunt instrument on one of the ends, the pollen is forced out in a 

 jet through a fine pore in the other inflated end. Mr. Leggett has seen 

 bees treading on the anthers, but could not get near enough to see the 

 pollen expelled. In the same journal, Vol. IX., p. 11, Mr. Bailey 

 describes how in Heterocentron roseum, " upon pressing the bellows-like 

 anther with a blunt pencil, the pollen was ejected to a full inch in distance." 

 On Lagerstrcemia as comparable with the Melastomads see Letter 689. 



2 Kosmos, XIII., 1883, p. 241. 



