I02 



ANGIOSPERMAE—DICOTYLEDONES 



protected from rain by closure of the corolla during dull weather. This also takes 

 place at night. The inner side of the corolla possesses nectar-guides in the form of 

 small whitish circles with brownish centres, from which alternating blue and whitish 

 longitudinal streaks turn to the base of the flower. At about its middle the corolla- 

 tube suddenly contracts, and from this point downwards it, and the filaments fused 

 with it, closely surround the ovary. Humble-bees can creep half-way into the flowers, 

 dusting themselves in younger ones from the dehisced anthers which closely surround 

 the still immature stigmas. In older flowers the style has elongated and its stigmatic 

 branches have become bent back so that their papillose inner surfaces will be touched 

 by those parts of humble-bee visitors which have taken up pollen. The arrange- 

 ments, in fact, are 

 such that insects of 

 a size proportionate 

 to the interior of the 

 flower inevitably ef- 

 fect crossing. Kerner 

 states that automatic 

 self-pollination is pos- 

 sible in later stages 

 of anthesis, for when 

 the flower closes some 

 of the pollen still 

 clinging to the an- 

 thers is transferred to 

 the internally project- 

 ing folds of the corolla, 

 and is subsequently 

 raised to the level 

 of the stigma by 

 elongation of the 

 corolla-tube. Closure 

 will then effect auto- 

 gamy. 



Warnstorf de- 

 scribes the pollen- 

 grains as yellowish 

 in colour, ellipsoidal, with a groove, delicately papillose, striated, on the average 

 50 fi. long and 25 /a broad. 



Visitors. — E. MoUer sent me the following from Sylt, of which only Nos. i, 2, 

 and 5 were able to get at the nectar (' Weit. Beob. u. Bl. u. Insekt. a. d. nordfr. Ins.,' 

 p. 238).— 



A. Hymenoptera. Apidae: i. Bombus cognatus Steph. 5 and 5, skg. ; 2. B. 

 derhamellus K. 5, do. ; 3. B. terrester Z., stealing nectar (up to beginning of October 

 1893) ; 4. Apis mellifica L. 5, do. ; 5. Psithyrus vestalis Fourcr. S, skg. B. Diptera. 

 All only po-dvg. (a) Syrphidae : 6. Platycheirus scutatus Mg. 5 ; 7. P. manicatus 

 Mg. 5. (3) Miiscidae: 8. Aricia incana Wied. 5; 9. Anthomyia sp. ; 10. Pollenia 

 rudis F. 



Fig. 261. Gentiaiia acaulis, L. (from Herm. Miiller's ' Alpenblumen '). 

 A. Entire plant. B. Longitudinal section of flower. C. Cross-section 



through base of do. (on the line ab). a, anthers; ca, calyx; co^ corolla; 

 Ji, filaments; ?x, nectary; crv, ovary; .s, nectar-passages; St, stigma jr, 

 upper end of nectar-guides. 



