APPENDIX A 



651 



A 



distal lobes. The syngenesious anthers form a dark purple tube, with a 

 terminal beak. The style bears below the stigma-lobes a ring of bristles, 



which acts like a sweep's brush upon the 

 pollen. The flowers are protandrous as 

 before. The filaments are curved and sensi- 

 tive, contracting on the stimulus of touch. 

 This is received by hairs radiating out 

 from them ; honey is secreted at the base 

 of the corolla (Fig. 501). 



The insect visitors are most commonly 

 bees. Inserting the proboscis into the tube 

 of a floret with stigma not yet receptive, the 

 filaments are stimulated ; they straighten 

 and contract, drawing the anther-tube 

 downwards. The bristles of the style thus 

 brush out the pollen at the moment the 

 insect is there, and it is deposited on his 

 body. If he then passes to a floret with 

 stigmas expanded cross-pollination is ensured. 

 But self-pollination is also possible by curva- 

 ture of the stigmas to touch the pollen 

 carried on the stylar brush. These examples 

 show how differences of detail in the florets 

 of the Tubuliflorae may be effective in 

 pollination : the fundamental facts being 

 a protandrous condition, and an aggregated 

 inflorescence. 



- 6 



B 



Fig. 501. 

 Stamens and style of Centaurca- 

 A, in the unstimulated, B, in the 

 stimulated state. The style in the 

 latter projects beyond the anthers, 

 and the pollen has been brushed out. 

 (After Strasburger.) 



(ii) Liguliflorae. 



(45) The Common Dandelion, or any Hawk-weed, will serve as an example. 

 The Dandelion (Taraxacum officinale, Web.) is a perennial herb, with massive 

 storage root, a rosette of radical leaves, and solitary, long-stalked heads. 

 The tissues are traversed by branched latex-tubes containing milky-juice. 

 The head consists of an involucre of bracts (Fig. 5° 2 » *), seated at the margin 

 of a naked, pitted general receptacle (gr.). Within are numerous ligulatc 

 florets, which are all alike, and have the same number and relation of parts 

 as in the Tubuliflorae. But the split ligulate corolla shows by its five teeth 

 at the distal end that it is composed of five petals. 



The pollination-mechanism is founded on protandry. The elongating style 

 sweeps out the pollen during the first stage of flowering ; the stigma then 

 expands and is receptive during the second stage. The heads expand in 

 sunshine, and intercrossing is possible by many different insects. Self-pollina- 

 tion is also possible by the recurved stigmas coming in contact with pollen 

 adhering to the style. It has, however, been found that in certain cases the 

 fruit of the Dandelion can be matured without any pollination at all, even 

 in buds from which the anthers and stigmas have been all cut away before 

 flowering. 



The fruiting head is the well-known Dandelion " clock," a type which is 



