280 



DEPOSITION OF POLLEN. 



the flower is its capacity for retaining the pollen brought to it. As might be 

 expected, flowers which are visited by insects agree but slightly in this respect with 

 those which are wind-pollinated. In all the instances where the pollen collected 

 by insects or birds has to be brushed off in adhesive crumbling masses, delicate 

 feathery stigmas, such as those of Grasses and many other plants which receive 

 powdery pollen by wind agency, would be of no use; but to the former, stigmas 

 possessing projecting edges, bands, and lobes, on which the insects as they pass must 

 leave their pollen, are better adapted. Usually close to the projecting edge there is 

 a depression which is filled with the deposited pollen. Thus, for example, the style 

 of Thunbergia (see fig. 27 9 16 ) ends in a funnel-shaped stigma whose edge projects 

 on one side like a shovel. When an insect strikes against this stigma on entering, 

 the pollen is received by this shovel and is at once deposited in the funnel-shaped 



Fig. 280. Deposition of the Pollen. 



i Flower of the Monkey Flower (Mimulus luteus). The same flower cut in half lengthwise with open stigma. The same 

 flower with closed stigma. * Pollen is deposited on the lower lip of the stigma by a proboscis passing in the direction of 

 the arrow. The stigma has closed in consequence of the stimulation : the proboscis passing in the direction of the 

 arrow opens the closed anthers and loads itself with pollen. The lower lobe of the stigma is only slightly raised so that 

 it does not come into contact with the proboscis which is being withdrawn in the direction of the arrow, and consequently 

 the pollen adhering to it does not reach the stigma. 1, 2 , and 8 natural size ; the others somewhat enlarged. 



depression. Insects which push their probosces into the flowers of the Violet 

 (Viola) inevitably strike against a little flap projecting from the lower side of the 

 capitate stigma (see figs. 279 1 > 2 ' 3 ), and when the proboscis is covered with pollen 

 this is left adhering to the inner side of the lobe. When the insect withdraws its 

 proboscis the lobe is pressed back against the stigmatic head, and thus the recently 

 received pollen is pushed into its cavity. The flowers of Irises possess stigmas with 

 the shape and colour of petals. They are bilabiate at their free end (see figs. 265 l 

 and 265 2 , p. 246). The upper lip of the stigma is curved, fairly large, and split into 

 two points, the lower lip is thin and forms a narrow membraneous lobe spread out 

 transversely. The path traversed by the humble-bee in obtaining the honey passes 

 under one of the bilabiate stigmas, and when it comes laden with pollen from 

 another flower it pushes down the thin flap of the lower lip, so that the pollen is 

 brushed from its back and deposited between the two lips. Many Scrophulariaceae 

 and Lentibulariaceae (Catalpa, Mimulus, Rehmannia, Torenia, and Utricularia), of 

 which the Monkey-flower (Mimulus luteus, see figs. 280 l > 2 > 3 ), may serve as a type, 



