BIOLOGY OF THE FLOWER 179 



out of the tube ; (3) the stigma-lobes then open, throw- 

 ing the pollen off, and exposing their inner surfaces for 

 pollination. 



As the disk-florets open successively from outside inwards, 

 two stages will be seen : (1) the old florets with stigmas 

 exposed, (2) younger florets with pollen only exposed. 

 A single insect-visit may thus readily convey pollen from 

 one floret to the stigma of another floret. Thus cross- 

 pollination of two degrees is possible : (1) a cross between 

 two florets of the same head, and (2) a cross between florets 

 on different Daisies. Honey, which is secreted by a ring- 

 like nectary round the base of the style, rises in the tube in 

 such quantity as to be accessible to short-tongued insects. 

 Thus the Daisy has gained many distinct advantages : (1) 

 conspicuousness, due to aggregation of many small flowers ; 

 (2) a large supply of honey protected from rain by narrow 

 tubes; (3) accessibility of pollen and honey to a great 

 variety of insect visitors ; (4) pollen presented so as to 

 secure cross-pollination in the case of insect-visits, or self- 

 pollination in their absence. 



The Coltsfoot. The bright yellow flower-heads of the 

 Coltsfoot may be found in January or February, when 

 insects are rare. The flowers appear before the leaves, and 

 from a single plant many flowering shoots of different ages 

 arise which prolong the flowering-period. Growth is main- 

 tained at the expense of food stored in its thick and often 

 long, underground stem, on which are the young leaves. 

 Each flowering shoot is covered by small, very hairy 

 bracts, and bears above a single capitulum. The bracts 

 of the involucre are in a single row and protect the florets 

 in the bud. Cut a capitulum vertically in two and note the 

 flat disk ; determine the different kinds of florets in the 

 head, and the interesting division of labour they show 

 (Fig. 123). 



The outer, strap-shaped florets are the most numerous 



m 2 



