COMPOSITAE 601 



437. Bidens L. 



Ray-florets sometimes absent in German species ; b'gulate, neuter, coloured like 

 the hermaphrodite tubular disk-florets. Stylar branches with lancet-shaped tips, 

 covered externally by strong sweeping-hairs, and beset with numerous stigmatic 

 papillae internally. 



1410. B. tripartita L. (Hildebrand, ' U. d. Geschlechtsverh'alt. b. d. Compositen,' 

 p. 67, Taf. I, Figs. 30-1; MacLeod, Bot. Jaarb. Dodonaea, Ghent, v, 1893, pp. 416-17; 

 Knuth, 'Bl. u. Insekt. a. d. nordfr. Ins.,' pp. 88, 157.) Ray-florets are almost always 

 wanting in this species. The diameter of the head is at most 1 cm. The sweeping- 

 hairs at the tip of the style are moderately long, the next below are shorter, and the 

 lowest are the longest. They brush out the 

 pollen from the anther-cylinder, which after- 

 wards becomes completely retracted into the 

 corolla-tube. The stylar branches then unfold 

 their papillose inner sides ; the corolla-lobes 

 so far spread out at the same time resume 

 a nearly vertical position ; and the pappus 

 bristles, with deflexed prickles on their outer 

 sides, spread out so that the diameter of the fig. '97- Bidens tripartita, l. (from 



, . . . . , - _,, nature). (i) Tip of style, with sweeping-hairs, 



head IS Ultimately increased tO 2^ Cm. Ihe in opening floret. (2) Ditto, of floret in female 



florets are at first yellow, but towards the end of s ' age : f stylar ^ anch f s rec " rve ?' and * eset with 



> ' stigmatic papillae internally. (x20.) 



anthesis assume an inconspicuous brown colour. 



Visitors. MacLeod (Belgium) saw 2 bees (Bombus and Andrena). 

 I noticed at Kiel 3 hover-flies (1. Melithreptus taeniatus Mg. ; 2. Platycheirus 

 manicatus Mg. ; 3. Syrphus balteatus Deg.), and a bug (Calocoris bipunctatus F.). 



1411. B. cernua L. (Herm. Muller, 'Weit. Beob.,' Ill, p. 88; MacLeod, 

 op. cit. ; Knuth, ' Bloemenbiol. Bijdragen,' ' Blutenbiol. Herbstbeob.') In this 

 species about 100 yellow florets are aggregated into a head. Hermann Muller 

 states that each disk-floret has a corolla-tube about i mm. long, with a bell 

 of about the same length and 1 mm. in width. In the first stage of anthesis 

 the pollen-covered anther-cylinder projects about 1 mm. from the bell, and in the 

 second stage the stylar branches (also 1 mm. long) diverge. The mechanism of 

 these branches agrees with that described for B. tripartita. The stigmatic papillae 

 are so broad that pollen-grains of the same flower may readily remain adhering 

 on the margin, so that automatic self-pollination is possible, as it is also in the last 

 species. There are three varieties. 



(a) discoidea Wimm. ; ray-florets absent ; 

 (5) radiata DC. (= Coreopsis Bidens L); large ray-florets; 

 {c) minima L. (=B. minima Z.); plant low (stem only 4-10 cm. high); 

 usually only one small head. 



Visitors. Herm. Muller saw only the honey-bee at Lippstadt. 

 At Kiel I observed a humble-bee (Bombus terrester L. 5, skg.) and a Muscid 

 (Lucilia cornicina F., po-dvg.). 



