3i8 



NATURE 



{Feb. 8, 1877 



From flowers so simple as those of G. lutea, which openly 

 oflfer their honey to all flying insects, but, in spite of their 

 extraordinary conspicuousness, are incapable cf securing 

 cross-fertilisation by the various visitors, the genus Gen- 

 tiana advances to such species as exclude from the honey 

 the majority of the less industrious visitors, and at the 

 same time compel the most industrious of the larger 

 Apidae, chiefly the humble-bees, to effect cross- fertilisa- 

 tion, whenever they fly from flower to flower. By what 

 modifications of structure this improvement has been 

 effected, may at once be seen in Fig. 96, which represents 

 a flower of Gentiana punctata, longitudinally bisected from 

 above to near the base. The petals, in G. lutea, nearly 

 completely separated, are here united, and form an 

 obliquely upright bell, wide enough to inclose the whole 

 body of any humble-bee. The pistil, just as in G. 

 lutea, stands exactly in the centre of the flower, and 

 is terminated by two re flexed branches of the stigma, 

 but the filaments, diverging in G. lutea, here incline 

 together, so that the anthers, developing some time 

 after the stigma, and dehiscing extrorsely, closely sur- 

 round the pistil somewhat beneath the stigma. The 

 honey being sepreted, as in G. lutea, by an annular swell- 

 ing at the base pf the pistil («, Fig. 97), every humble-bee 

 is induced to creep towards the base of the bell-shaped 

 corolla, and, when doing so, first touches the stigma and 

 dusts it with pollen of previously-visited flowers, thus 

 eff"ecting cross-fertilisation ; then with the same portion 

 of its hairy body it touches the anthers and charges itself 

 with fresh pollen. The exclusion of the majority of use- 



FlG. ICO. 



I'lG. lOI. 



Fig. 



less visitors from the honey is effected by the base of the 

 corolla being constricted, and the base of the filaments 

 united with it (as far as ch, Fig, 96) ; the narrow interstice 

 between the ovary and the corolla being thus divided by 

 the filaments into as many narrow channels as there are 

 petals and filaments (in G. punctata commonly seven, in 

 G. acaulis, excisa, and others five), By these narrow 

 channels humble-bees may easily pass their proboscides 

 as far as the honey, whereas saw-flies, flies, and most 

 beetles are unable to reach the honey. 



Thus the variety of visitors has been greatly diminished ; 

 but the humble-bees, for which alone the honey is reserved, 

 are hence induced to make more eager and frequent visits ; 

 and, as by these visits not fortuitously, as in G. lutea, but 

 regularly pollen is brought from one flower to the stigma 

 of another, cross-fertilisation in the species of this group 

 is far more certain than in G. lutea; and the possibility of 

 self-fertilisation, indeed, seems to have been lost. 



Of twenty-six species of Gentiana inhabiting Germany 

 and Switzerland, eleven belong' to the present group, which 

 must almost necessarily be cross- fertilised by humble-bees ; 

 naniely, besides the three above-mentioned species in- 

 habiting the plain and lower mountain region, the fol- 

 lowing eight Alpine ones : G. punctata, purpurea, pan- 

 mjwzra, asclepiadea, Fr(elichii,frigida, acaulis, and excisa. 

 But hitherto only three of these eleven species have been 



actually observed to be visited and cross-fertilised by 

 humble-bees, namely, G. acaulis, by Ricca (" Atti della 

 Soc. Ital, di Sc. Nat.," xiv. 3, 1871), G. pneumonanthe 

 (H. Miiller, " Befruchtung," p. 333), and G. excisa^ by 

 myself. 



3. Alpine Species of Gentiana, adapted at the same time 

 to Apidce and to Lepidoptera, — Whilst in the foregoing 



Fig. 103. 

 Figs. 103-105. — Gentiana nana, Wulf. — Fig. 103. — F'ower seen from above 

 (7 : i). t'lG. 104. — The same flower bisected longitudinally. Fig. 105. 

 — A piece of the corolla, with petals, protecting hairs, stamens, and nec- 

 taries (7 : 1). 



group Diptera and other useless visitors are prevented 

 from gaining the honey by the base of the corolla being 

 constricted and by the filaments dividing the interstice 

 between the corolla and the ovary into narrow channels, 

 in the present group {G. tenella, Fig. 98-102; G. nana, 

 Fig. 103-105) the same effect has been attained by the 

 entrance to the tubular corolla being barred by hairs 

 {pr Fig. 98, 99, 102-105), between which only four or five 

 small openings {p, Figs. 99, 103) are to be seen. The 

 corolla, in the previous group wide enough to inclose the 

 whole body of a humble-bee, is here so narrow that any 

 proboscis attempting to reach the honey will graze the 

 stigma and the anthers, and, when passing from flower to 

 flower, will effect cross- fertilisation. But only Apidae will 

 be enabled to thrust their proboscides between the pro- 

 tecting hairs, and only Lepidoptera have proboscides slen- 

 der enough to penetrate the small openings. Thus, in these 

 flowers the visits of Lepidoptera are useful for the cross- 

 fertilisation of the plant, while in the foregoing group 

 they are useless. 



Most probably the present group is not descended from 

 the foregoing ; besides the narrowness of the corolla and 



Fig. 104. 



Fig. 105. 



the protecting hairs, the position of the nectaries is so 

 peculiar to this group, that it is rather to be considered 



' I found, in the Alps, G. excisa visited and cross-fertilised by Bombiis 

 lapponicus, ^.,and B. mendax, Gerst. Once, in the Albula Pass, July 28, 

 1876, I saw a moth, Plusia hochentvarthi, creeping into a flower and sucking 

 its honey, but without touching stigma or anthers. Also some small Dipttra 

 and three specimens of a small beeUe, Haltica melanostoma, Redt., can Only 

 be registered as useless guests. 



