260 THE FERTILISATION OF FLOWERS. [PART III. 
labellz for a short time (one to two seconds) in order to add to the liquid 
non-nitrogenous food some solid nitrogenous matter in the shape of pollen- — 
grains, In inserting its proboscis into the tube, the conical prolongation of 
the head comes in contact with the middle-sized reproductive organs, while the 
proboscis itself touches the shortest ; the longest organs come at timesin contact _ 
with the ventral surface of the fly, but very often fail to do so ; and so this fly, 
as a rule, only performs two-thirds of the legitimate work of fertilisation. 
Two other Syrphide, Helophilus pendulus, L., and H. trivittatus, F. (proboscis. 
6—7 mm. long), alight upon the longest reproductive organs, and fertilise all 
three kinds of flowers legitimately ; so also does Volucella plumata, L., whose 
proboscis is 7—8 mm. long. Several smaller Syrphide, whose proboscis is too 
short to reach the honey, viz. Syritta pipiens, L. (proboscis 3 mm.), Syrphus — 
balteatus, Deg. (2 mm.), and Melithreptus teniatus, Mgn., feed on the pollen, — 
which they may chance to carry to the stigmas; but they are as likely to _ 
perform illegitimate as legitimate fertilisation. The same holds good of Halictus 
eylindricus, F. ¢, which has likewise too short a proboscis to reach the honey, 
and only collects pollen on this flower ; and also of some very small insects, _ 
Nanophyes lythri, F., Meligethes, and Thrips, which creep down into the tube, — 
and of a species of Capsus which runs about indiscriminately on the leaves and — 
also on the flowers of the plant. Va 
Two butterflies also, Rhodocera rhamni, L., and Pieris rape, L., are to be . 
seen rather abundantly on the flowers of the Loosestrife. The butterfly, sitting — 
upon one flower, thrusts its proboscis (15 mm. long) into the next; it thus — 
touches the shortest organs regularly with its proboscis, but seldom the middle- — 
sized ones, and the longest scarcely ever, but the middle-sized and longest _ 
organs of the flower on which it is seated come in contact with the ventral 
surface of its body. y 
In the following list, those insect-visitors which regularly accomplish cross-— 
fertilisation in its three forms are marked with (!) ; those which as a rule only — 
effect one or two forms of crossing are printed without special mark ; and 
those which only occasionally fertilise the plant, and perform illegitimate ~ 
as often as legitimate fertilisation, are placed in parentheses. 
A. Hymenoptera—Apide : (1) Cilissa melanura, Nyl. $ 9! s. and e.p., ab. 3 
(2) Saropoda rotundata, Pz. ¢ 9!s., not rare; (3) Apis mellifica, L. $! s. 3 
(4) B. terrestris, L. §!s.; (5) B.agrorum, F. §!s.; (6) B. silvarum, L. $! 5. 5 
(7) Megachile centuncularis, L. ¢!s. ; (8) (Halictus minutissimus, K. 2, s.); 
(9) (H. eylindricus, F. 2,¢.p.). B. Diptera—Syrphide : (10) Rhingia rostrata, 
L,, s. and ¢.p.; (11) Helophilus pendulus, L.!s.; (12) H. trivittatus, F.!s. 5 
(13) Volucella plumata, L.!s.; (14) (Syritta pipiens, L., fp.) ; (15) (Syrphus_ 
balteatus, Deg., f.p.) ; (16) (Melithreptus teeniatus, Mgn., f.p.). C. Lepidoptera” 
—Rhopalocera: (17) Rhodocera rhamni, L.,s., ab.; (18) Pieris rape, L.,s., ab, 
D. Coleoptera—(a) Curculionidae : (19) (Nanophyes lythri, F.) ; (b) Nitidulide = 
(20) (Meligethes). E, Thysanoptera—(21) (Thrips). F, Hemiptera—(22) 
(Capsus). See also No. 590, 11. . 
* 7 
Lythrum Graeffert, Ten., is, like Z. Salicaria, trimorphic; DL. 
thymifolia, L., is dimorphic, and L. hyssopifolia, L., homomorphie 
(Darwin, No, 154). 
Besides Lythrum, Nesea, Commers., and Lagerstremia, L., have 
