- PART III. | THE MECHANISMS OF FLOWERS. 339 
are 4to 54} mm. long. About thirty-five to seventy-eight florets 
unite in a capitulum, which inferiorly is scarcely 10 mm. in 
diameter. The tubes of the florets point outwards more and more 
the nearer they stand to the edge, and the whole capitulum when 
seen from above appears as a red surface 25 to 30 mm. in diameter. 
- It is also conspicuous when seen from the side. Otherwise the 
structure of the flowers agrees with that of Cnicus arvensis ; but 
_ the list of insect-visitors is limited by the greater depth of the 
_ throat of the corolla. 
Visitors : A. Hymenoptera—Apide: (1) Bombus agrorum, F. &% 2, s. ; 
_ (2) B. lapidarius, L. § g,8., both ab. (the males as late as October 2) ; (3) 
' Halictus cylindricus, F. ¢,s.; (4) Osmia fulviventris, Pz. ?, cp. ; (5) Stelis 
_ aterrima, Pz. 2,8. B. Diptera—Syrphide ; (6) Eristalis tenax, L., s. and f.p., ab. 
_ ©. Lepidoptera—(7) Pieris napi, L., s. ; (8) P. rape, L. See also No. 590, 11. 
246, CARDUUS ACANTHOIDES, L.—The capitulum is even more 
conspicuous than in C. crispus, since the narrow segments of the 
- corolla are 7 to 8 mm. long (instead of 4 to 53). ‘The honey is 
more easily accessible, for the throat of the corolla is wider than in 
C. crispus and only 2 mm. long (instead of 23 to 3). Moreover 
C. acanthoides (at Miihlberg, in Thuringia) grows associated in 
much greater numbers than C. crispus (at Lippstadt). These three 
circumstances account for the very much greater number and 
variety of insect-visitors in the case of CO. acanthoides, whose flower 
_ has otherwise the same structure as that of C. crispus. 
A. Hymenoptera—(a) Apide: (1) Bombus lapidarius, L. § ; (2) B. silva- 
rum, L. § 2; (3) B. muscorum, F. §; (4) B. pratorum, L. ¢; (5) Dasypoda 
_hirtipes, F. 9; (6) Cilissa tricincta, K. (leporina, Pz.), 2; (7) Halictus inter- 
' ruptus, Pz. ¢; (8) H. nitidiusculus, K. ¢ 9; (9) H. albipes, F. ¢, ab. ; (10) 
| # quadricinctus, F. ¢ 9, very ab.; (11) H. rubicundus, Chr. ¢ 9, freq. ; 
| e.?) H. longulus,Sm. ¢ 2; (13) H. cylindricus, F. ¢; (14) H. quadrinotatus, 
. XK. dg, scarce; (15) H. maculatus, Sm. ¢ 9; (16) H. minutus, K. ¢; (17) 
_H. lucidulus, Schenck, ? ; (18) H. Smeathmanellus, K. 9, all (1—18) s., only; 
_ H. quadricinctus, , ¢.p. also ; (19) H. leucozonius, K. ¢ 9, s. and c.p. ; (20) 
Osmia spinulosa, K. ?, very ab., s. and c.p. ; (21) O. enea, L. g, 8. 3 (22) O. 
aurulenta, Pz. 9,s. and c.p.; (23) O. fulviventris, F. 9, s. and cp. ; (24) 
I Megachile lagopoda, K. 2 ¢,s. and c.p.; (25) M. centuncularis, L. ¢,s. ; (26) 
_ M. versicolor, Sm. 9, s. ; (27) Chelostoma campanularum, L. ? ¢, s.and cp. ; 
| (28) Heriades truncorum, L. ? ¢, 8. and ¢. p.; (29) Stelis pheoptera, K. 9, 
- not rare ; (30) St. aterrima, Pz. 9 ¢, freq. ; (31) St. breviuscula, Nyl. 9 ; (32) 
Prosopis punctulatissima, Sm. 9. By far the most important visitors are the. 
bees with abdominal collecting-brushes, I have found Osmia spinulosa on 
Carduus acanthoides in the same abundance, and working with the same dili- 
gence, as Megachile on Onopordon. (b) Vespide : (33) Cerceris variabilis, 
Schrk. 9,s. B. Diptera—(a) Syrphide: (34) Eristalis arbustorum, L., s. ; 
: : Z2 
