580 ANGIOSPERMAEDICOTYLEDONES 



1322. P. albus Gaertn. (=Tussilago alba Z., the hermaphrodite plant, and 

 T. ramosa Hoppe, the female plant). (Herm. Miiller, 'Fertilisation/ pp. 334-5, 

 ' Alpenblumen,' pp. 455-9.) This species is dioecious, with four different forms 

 of floret. In the heads of the female stocks there are both nectar-secreting and 

 nectarless sexual florets. In the heads of the male stocks there are often only 

 nectar-secreting and pollen-producing florets, but about as frequent as these are 

 heads which also include one or two florets producing neither nectar nor pollen. 



Visitors. Herm. Miiller (Alps) observed 6 flies, Lepidoptera (only 2 species, 

 but very numerous individuals), 2 beetles. 



1323. P. fragrans Presl. 



Visitors. Burkill observed the following Diptera on the Yorkshire coast 

 (' Fertlsn. of Spring Fls.'). 



{a) Muscidae: 1. Lucilia cornicina F. ; 2. Onesia cognata Mg., po-dvg. ; 3. O. 

 sepulcralis Mg., do. (6) Syrphidae: 4. Eristalis pertinax Scop.; 5. Melanostoma 

 quadrimaculata Verral. 



1324. P. frigida Fries. According to the observations of Lindman on the 

 Dovrefjeld, this northern species is dioecious, though to a lesser degree than P. albus. 

 The florets are odourless. In male heads the ray-florets are purely female: the 

 reddish stylar branches project from the large but few male florets, and have not 

 only the function of sweeping out pollen, but also serve to attract insects. The 

 female heads are smaller than the male : their disk-florets possess vestigial stamens, 

 but their ray-florets are purely female. Ekstam gives the diameter of heads examined 

 by him in Nova Zemlia as about 10 mm. According to Andersson and Hesselman 

 ('Bidrag til Kanned. om Spetsbergens o. Beeren Eil. Karlvaxtflora,' pp. 11-12), 

 separate sexual forms are found in Spitzbergen, as on the Dovrefjeld. The male 

 heads are 12-5-16 mm. long; the ligulate corolla-lobe of the ray-florets is strongly 

 developed, and projects beyond the style. The female heads are only 11-14 mm. 

 long : the ray-florets possess a shorter recurved corolla-lobe. The florets are bright 

 reddish, the male ones being somewhat more strongly coloured. The fragrance 

 is tolerably well marked (cf. Ekstam, ' Bliitenbiol. Beob. a. Spitzbergen,' p. 6). 

 Ripe fruits are but rarely formed in Spitzbergen, though De Geer (according to 

 Nathorst) observed some on August 30, 1882. 



Visitors. Ekstam saw a medium-sized fly in Nova Zemlia, but no visitors 

 in Spitzbergen. 



(3) Tribe Aster oideae Less. 



Stylar branches linear, pointed, almost flat externally, otherwise as in the 

 last tribe. 



418. Aster Tourn. 



Ray-florets uniseriate, female, usually differently coloured from the yellow disk- 

 florets. Stylar branches broadened, covered with sweeping-hairs above, and beset 

 by stigmatic papillae laterally and internally: their tips almost always inclined 

 together in hermaphrodite florets. 



Kerner states that the stylar branches of the ray-florets come into contact 

 with the pollen-masses thrust out from the disk-florets. He also says that automatic 



