THE DICOTYLEDONES 



1959 



flower at this stage will be liberally dusted with pollen. In the second stage 

 in anthesis the style elongates further and the receptive stigmatic papillae 

 become exposed above the bell-shaped corolla, so that an insect visiting 

 the flower will now dust ofl" any pollen it has previously acquired on to the 

 papillae. Such an arrangement ensures that if insect visitors have been 

 sufficiently numerous to remove all the pollen from the sweeping hairs, 

 cross-pollination must occur. On the other hand if visits have been infre- 

 quent self-pollination must occur as a result of an insect visit. Self-polli- 

 nation cannot take place in the absence of an insect visit, but geitonogamy 

 undoubtedly occurs, for the stigmatic branches spread out so that they 

 occasionally touch the hairs on adjacent styles. The nectar is secreted from 

 the base of the style and the flowers are visited mainly by butterflies. 



In Petasites fragrans (Fig. 1888) (Winter Heliotrope) belonging to the 

 tribe Senecioneae, the capitula occur in two forms, quite diflerent from one 

 another in appearance. In the one there are numerous pseudo-hermaphro- 



FlG. 1888. — Petasites fragrans. Winter 

 Heliotrope. A, Female ray floret. 

 The ovary is ruptured and the ovule 

 projects. B, Nectariferous floret 

 from a female capitulum. C, 

 Pseudo - hermaphrodite (male), 

 nectariferous floret from a male 

 capitulum. {After Kiuith.) 



dite pollen-bearing florets on the disc and a smaller number of female 

 florets in the rays. In the other type the condition is reversed. 



The male florets usually possess nectar and the pollen is swept out of the 

 florets by a columnar style beset with sweeping hairs: the ovary however is 

 vestigial. The corolla is tubular below but expanded above into a bell- 

 shaped structure with four lobes. The female florets are nectarless and 



