PART 111. | THE MECHANISMS OF FLOWERS. 309 
the abortion of one stigma an adaptive modification in progress 
_ and not yet perfected. — 
M (1) Bombus rupestris, L. 9 (12—14) ; (2) B. lapidarius, L. ¢-§ ? (8—14), 
' ab., (¢ as late as October 2); (3) B. agrorum, F. § @ (12—15), all three 
_ species sucking. See also No. 590, II. 
211. ScaBiosA (KNAUTIA) ARVENSIS, L.—In fine weather the 
flowers, owing to their great conspicuousness and their easily 
accessible honey and pollen, are visited by very miscellaneous 
‘insects in great numbers. Cross-fertilisation is ensured by markedly 
_proterandrous dichogamy, and in the unlikely event of insect-visits 
not taking place, self-fertilisation is very unlikely to occur. 
Fic. 108.—Scabiosa arvensis, L. 
1.—Hermaphrodite flower in first anes stage, after removal of one lobe of the corolla (x 34 
2.—Ditto, in second (female) stag 
3.—Female flower, after removal of one lobe of the corolla. 
a, stigma; b, anther still within the flower; ¢, ditto, dehiscing ; d, ditto, empty and shrivelling 
a re, abortive anther. 
2 
About fifty flowers unite in a capitulum which may be hemi- 
_ Spherical or only slightly convex, and become gradually larger 
_ from the centre to the margin by an increasing development of the 
_ outer lobe of the corolla. While in the central florets the tube is 
i= only 4 to 6 mm. long, and the lobes of the corolla, which are all 
similar, only 3 to 4mm. long, in the marginal florets the tube is 
_7 to 9 mm. long, the external lobe of the corolla 6 to 11 mm., each 
of the two ical lobes 4 to 7 mm., and the internal lobe wale 3 to 
4mm. long. 
____Inpite of the length of the tube the honey is easily accessible 
| toavery large number of insects of the most various orders ; for 
