480 



NATURE 



[Oct. 10, 1872 



runners. Do the white pea-blossoms attract night-flying 

 insects ? 



Lathyrus odoraius. — This is, so far as the above 

 functions .are concerned, so like Pisum, that it is scarcely 

 worth while to ducll on the differences. In colour and 

 smell, of course the difference is great, and consequently 

 in the attractions for different insects. The changing 

 position of the pedicels ; the brush to the style ; the 

 free or partially free stamen, and the nectar inside the 

 case of the staminal tube, and the openings into that 

 tube, are the same (see Fig. 6). 



Lallsynis macrorhizus, is, so far as I have observed 

 it, similar. 



Lathyrus pisij'orim's is like the other Lathyri in the 

 above points, except that in the long raceme of tlowers, 

 the whole peduncle, andnot only the pedicels of the scp.i- 

 rate tlowers, is pendent in the bud. It stiffens and 

 becomes upright as the blossoms open, and the pedicels 

 also stiffen and become horizontal. After tlowermg the 

 peduncle remains stiff and upright, but the pedicels droop. 



Lathy I us pyatcnsis. — The fertilising apparatus is the 

 same as in the above Lathyri. 



Lathyrus sylvestris, or latifolius, or Everlasting Pea. — 

 Here the many-flowered raceme is itself upright, whilst 

 the pedicels bend, straighten themselves, and again bend, 

 as in Pisum (sec Fig. 7). In the fertilising apparatus the 

 mechanism is the same as above described, with the ex- 

 ception that there is a very decided obliquity in the keel 

 and in the style, though not so decided as in the following. 



Ltithyrus i^randijhvus. — In this flower the peculiarities, 

 as distinguished from the above-mentioned Lathyri, are as 

 follows : — The pedicels bend, straighten, and bend them- 

 selves again, as above mentioned ; but the effect generally, 

 if not universally, is to make the large showy vexillum, and 

 not the keel, horizontal. The vexillum, consequently, and 

 not the keel, would be the natural alighting place for an in- 

 sect. The wings are at right angles to the vexillum, and the 

 recurved point of the keel projects between them and over- 



hangs the vexillum. An insect alighting on the vexillum, and 

 thrusting itself towards the nectary, must push the wings, 

 and with them the keel, upwards, and make the style and 

 the pollen come out ; but they will come out downwards 

 on to the back of the insect, and not on to his thorax or 

 belly. 



Another peculiarity is that tlie keel, and with it the 

 style, is very oblique, and the upper part is flattened, and 

 is twisted so that the back of the style does not press 

 against the keel. Corrolatively both sides of the style are 

 well furnished with hairs, and both sides equally operate 

 in sweeping the pollen out of the keel. In this respect 

 Lathyrus grandiflorus seems to show a gradation towards 

 Phaseolus. 



Phasc-olu! inultiJlorus,ox Scarlet Runner. — In the posi- 

 tion of the blossom whilst flowering, in the nectar-holding 

 cavity of the staminal tube, and in having an entrance 

 to the cavity by the separation of the tenth stamen, this 

 flower resembles Lathyrus and Pisum, but it offers the 

 following peculiarities (see Fig. S) : — 



The pedicel of the bud before flowering is perpendicular 

 and stiff, and the bud consequently upright ; the pedicel 

 becomes rather more horizontal as the flower opens, and 

 in blossom the wings are horizontal, whilst after flowering 

 the pedicel becomes quite horizontal, and the pod gradu- 

 ally sinks, and ultimately becomes pendent. Corrola- 

 tively, there is no large pent-house of a calyx, as in Pisum, 

 to protect the young blossom ; but the same object seems 

 to be effected by the smooth, strong, thick vexillum, the 

 edges of which are in the bud closed valvately over 

 the tender folded interior petals ; whilst in the bud 

 of Pisum the whole of the petals, whilst sheltered by the 

 calyx, are tender and unclosed. The young pod of Phase- 

 olus, also unlike the thin glabrous pod of Pisum, is thick 

 and covered with short hairs. 



The keel, which in some Lathyri is very oblique, is in 

 Phaseolus so twisted, and has its edges so joined, as to 

 form an imperfect tube containing the stamens and style ; 

 it makes with them nearly two complete spiral turns, and 

 its mouth points obliquely downwards. The stiff, elastic 

 style is clothed with stiff hairs or bristles, forming a cir- 

 cular brush at the point in the tube where it is surrounded 

 by, and in contact with, the moist, sticky pollen of the 

 mature anthers. The stigma is on the lower side of the 

 style, just appearing at the mouth of the tube, is sticky, 

 and is clothed with fine hairs. 



The filament of the tenth stamen is entirely separate 

 from the others, and is furnished with a sort of tooth or 

 appendage on the outside, upon pressing which the stamen 

 is drawn back, and free access is given to the nectar- 

 holding cavity. On the other hand, there is no such 

 aperture on each side of the base of the tenth stamen as 

 there is on each side of the base of the semi-adherent 

 filament in Pisum and Lathyrus. 



A bee lighting on the wings, or rather on the outer 

 wing, opens for himself a way to the base of the flower. 

 At the same time, the wing being attached to the spiral 

 tube of the keel, he pulls it outwards, the consequence of 

 which is that the stiff style is thrust outwards and at first 

 downwards, so that the sticky stigma first touches the 

 entering insect and sweeps from his proboscis any pollen 

 he may have brought from other flowers. As he passes 

 further, the stigma protrudes further, turns upwards, and 

 the brush of the style, loaded with the sticky pollen of 

 its own anthers, sweeps against, and leaves its load on, 

 his proboscis, with which he departs for other flowers. 



The mechanism of this flower is truly wonderful. For 

 further details I coifld refer to papers by Mr. Darwin in 

 the Gardciier''s Clironiiic of October 24, iS57,and Novem- 

 ber 14, 185S, and to thenotes of my own in the y4««(i/.yrt//(/ 

 Maf^azinc of Natural History, October 1868. 



Phaseolus vulgaris is similar to P. mtdtiflonis. 



T. H. Farrer 



{To be continued.) 



