July 7, 1874] 



NATURE 



169 



FERTILISATION OF PAPILIONACEOUS 

 FLO WERS—COROSILLA 



TN Nature, vol. vi. pp. 478 and 49S, you inserted a 

 ■'■ paper of mine in which an attempt was made to draw 

 certain general conclusions concerning the fertilisation of 

 papilionaceous flowers from the examination of a few 

 genera, chiefly English : and in that paper I stated that 

 the foreign genus Coronilla presented peculiar difficul- 

 ties. I have since then been stimulated by Mr. Darwin's 

 kind interest to examine Coronilla more carefully, and 

 now send you the results. 



The ultimate result of these gcner.alisations was that in 

 all the following particulars, viz. the position and motion 

 of the flowers and the peduncle, the cohesion of the petals, 

 the cohesion of the stamens (so remarkable a feature in 

 this tribe) ; the structure and character of the filaments, 

 of the anthers, and of the pollen, the structure of the 

 style and stigma ; and the place where nectar is secreted ; 

 the parts and functions are so organised and correlated 

 as to induce and compel insects, generally bees, in visiting 

 the flowers for nectar, to carry away with them pollen 

 from one flower and bear it to another. 



One, perhaps the most striking, of the generalisations 

 in question was as follows : — 



" The degree to which the cohesion of the stamens is 

 carried, so remarkable a feature in this tribe, seems to 

 depend on the necessity for access to nectar. In those 



Fir,. I.— Coronllli 



flovers in which the stamens are monadelphou5, viz. 

 Ulex, Sarathaumus, Genista, Cytisus, Ononis, Lupin, 

 theie is no symptom of nectar within the staminal tube, 

 no space for it, and no access to the interior. In some, 

 at any rate, of these, viz. Ulcx, Ononis, and Lupin, the 

 bees certainly resort to other parts of the flower. On the 

 o'.her hand, where the tentli stamen is entirely free or 

 where it is separated from the others at the base, so as to 

 give an insect access to the interior of the staminal tube, 

 there is nectar within this cavity." 



To this generalisation the two species of Coronllli 

 which I had examined, viz. C. varla and C. glauca, seemed 

 to form an exception. In them the tenth stamen was 

 always separate ; but there was no aperiure at the base 

 of the staminal tube, no nectar within the staminal tube, 

 and no space for it, the base of the staminal tube fitting 

 as closely round the pistil as it does in those papilionaceous 

 flowers in which the tenth stamen is not separated from 

 the rest. 



I have since had an opportunity of examining several 

 species of Coronilla, and of watching large plants of C. varia 

 (Fig. 1) and C. cmcrus (Fig. 1) in l^uU llower. In all these 

 llowers there is a peculiar structure of the petals. The claw 

 of the vexillum is thin, sometimes prolonged and straight 

 as in C. cimrus ; sometimes shorter and curved as in 

 C". varid. The claws of the other petals cohere so as to 

 form a channel, in which the staminal tube lies. liut in 

 all cases there is, immediately a'lore the calyx, a large 



open space between the claw of the vexillum and the 

 claws of the other petals so as to have free access from 

 the outside to the inside or the inside to the outside of the 

 flower. 



One hot day last August I watched a bee rifling the 

 flowers of C. varla in the regular way. He settled as 

 usual on the lower flowers of the crowded umbel first, 

 resting on the wings and keel, and went rapidly round and 

 up the umbel. The plant was a large one, and he must 

 have been there more than half an hour. He did not 

 seem to be taking pollen. What could he be doing ? for 

 there was no semblance of nectar either inside the base of 

 the petals or calyx or inside the staminal tube. On ex- 

 amining the flower carefully with a glass the oulsidc of 

 the calyx, which is thick and fleshy, appeared to be 

 covered with shining glands or vessels, sometimes I think 

 moist, but always yielding copious liquid on very slight 

 pressure. Could this be what the bee was seeking 'i 

 On a subsequent day I again watched a similar bee 

 rifling the flowers, and at last distinctly saw his pro- 

 boscis, which had entered as usual by the front of the 

 flower, protruded outwards through the gap between the 

 claws of the petals and sweep the outside of the caly.x. 

 Here then was an answer to my difficulty. The nectar 

 for which the bee sought the flower, and in getting which 

 he benefited the plant by carrying pollen from flower to 

 flower, was not in any of the usual places inside the 

 flower, but outside the calyx, while there was a very 

 peculiar construction of the petals giving access to it. 

 Instead of proving an anomalous exception to the gene- 

 ralisations I have quoted above, it turns out to be another 

 curious illustration of the various ways in which the same 



function of secreting nectar and of attracting the bee to it 

 in the manner requisite for fertilising the flower is effected 

 by different organs. That the outside of the calyx should 

 secrete nectar and that there should be a peculiar window, 

 out of which the bee, having entered by ttie regular door, 

 and liaving in so doing dusted himself with pollen, should 

 be able to get at the nectar, is surely a remarkable 

 siiecialisation, and also a remarkable confirmation of the 

 result of generalisations I had previously made. 



Since then I have examined some other species or 

 varieties of Coronilla, viz. Coronilla cinerns, a very pretty 

 free flowering garden shrub or creeper, a variety of this 

 named Coronilla eincrus lutcsccns, C, montana, and C. 

 minima. 



In Coronilla emcrns the claws of the petals are much 

 prolonged, so as to make the whole flower much longer 

 than in the other species (see Fig. 2). The structure of 

 the staminal tube is like that of Pisum, Lathyrus, Robinia, 

 (Sic, in having a large cavity at the base filled with water, 

 and large apertures on eaca side of the base of the tenth 

 stamen, by which the bee's proboscis can reach the nectar. 

 The long tube or channel formed by the claws of the 

 petals is such as to lead the bee's proboscis directly to 

 these apertures ; and I have this spring distinctly seen a 

 humble-bee getting the nectar in this way. The aperture 

 between the claws enabled me to see the bee's proboscis 

 going right down to the base of the staminal tube. On 

 the other hand there is no appearance whatever of nectar 

 or of glands containing nectar outside the calyx. 



In C'. einerus lutcsccns the structure is the same, except 

 that there is a curious little excrescence on the inside of 

 the claw of the vexillum just above the calyx. Does it 



