56 



HARD WICKE'S SCIENCE- G OSS IP. 



expansion similar to a nettle-sting. There is but little 

 chlorophyl, a large portion of the bract being occu- 

 pied by air-spaces, into which numerous long, narrow 

 stomata open. The corolla is salver-shaped, slightly 

 oblique, and of a clear Nankeen yellow, the colour 

 being somewhat brighter round the throat. In some 

 forms the throat is a dark chocolate-brown, almost 

 black, while in one variety the limb is pure white 

 with a dark throat. The stamens are four in number, 

 and are situated far down in the tube of the corolla, 

 the interior pair being considerably shorter than the 

 exterior pair. The filament is inserted into the dorsal 

 portion of the connective, a short distance from the 

 base of the anther, thus giving the ventral face of the 

 anther a slight inclination forwards and upwards. 



Fig. 45. Diagram of flower of Thunbergia alata (vertical 

 section). 



The anthers adhere by the ventral suture, the pro- 

 jecting margins of the lobes being densely bearded 

 with hairs of a peculiar and interesting form. They 

 are slender and clavate, consisting of numerous joints. 

 The lower are oblong, three or four times as long as 

 broad. Proceeding from the base upwards, the joints 

 become shorter, thicker, and more rounded, and with 

 deeper constrictions, giving a beaded appearance, the 

 uppermost one being frequently divided by vertical 

 septa into two or three. These topmost cells are 

 some twice or thrice the diameter of what I may term 

 the stem of the hair, the whole of which, from base to 

 summit, is finely tuberculated, the tubercles increasing 

 in number and size from below upwards. A trace of 

 this tuberculation occurs also on the hairs of the bract, 

 but to a very much smaller degree. The pollen, 

 which, like the anthers and the anther hairs, is almost 

 white, is spherical, and has several broad, flat, spiral 

 grooves winding round it in opposite directions, pro- 

 ducing a very curious appearance. The pistil is long 

 and slender, passes up between the interior and 

 shorter pair of stamens, and, like them, is closely 



! adpressed to the back of the corolla tube. The 

 stigma, which is situated a short distance above the 

 upper stamens, appears to consist of two parts. The 

 upper portion is the style slightly flattened and curved 

 round into a kind of a narrow funnel, at the base of 

 which, and on the front of the style, is a semicircular 

 cup-shaped body, which seems to be a further develop- 

 ment of the stigma, as I have observed numerous 

 pollen-grains adhering to its viscid edges. The con- 

 cave surface of this cup is upwards, the convex down- 

 wards. Thus it appears that every precaution is taken 

 to avoid self-fertilization. The corolla is almost erect, 



Fig. 46. Anther-hair and pollen-grains of Thunbergia x 200. 



Fig. 47. Hairs of bract of Thunbergia X 50. 



the stamens densely bearded on the ventral or front 

 side, with hairs pointing downwards, which hairs, still 

 further to retain the pollen from any accidental dis- 

 turbance from wind, Sec, are club-shaped, thickened 

 at the apex, and closely tuberculated, while the 

 pollen-grains themselves have spiral grooves to 

 increase their tenacity to the hairs. Again, the stig- 

 matic surface is turned directly away from the pollen, 

 so that it is scarcely conceivable that self-fertilization 

 could take place. Suppose an insect with a long pro- 

 boscis visits the flower, its proboscis passes down- 

 wards freely to the base of the corolla ; on with- 

 drawing it, the trunk cannot fail to brush upwards or 

 backwards some of the anther hairs, and in so doing 

 set free some of the pollen which adheres. The 

 horizontal and non-stigmatic portion of the pistil 

 being downwards, receives none of the pollen. The 

 insect visits another flower, and thrusts its proboscis, 

 laden with pollen, into the corolla. In so doing, the 

 stigma being in a narrow portion of the tube, is 

 nearly certain to intercept some of the grains, and 

 thus ensure fertilization. Even should this fail, 

 touching the base of the style causes it to bend for- 

 ward, and thus be ready for the next comer. The 



