424 THE FERTILISATION OF FLOWERS. [PART ITI. 
between them. The five narrow slits between the stamens, near 
their base, are thus the only means of access to the honey, and the 
insect must make its way into the funnel between the corolla and 
the stamens, and then insert its proboscis into one of the slits. 
Since the stamens dehisce extrorsely, an insect acting in this way, 
unless it be too small, must be dusted with pollen; and the two | 
branches of the stigma, standing well above the anthers, and 
stretching outwards over them, are touched before the anthers by 
the insect. In absence of insects, self-fertilisation can easily occur ; 
for if the flower hangs down, or if the corolla withers and falls off, 
the pollen readily falls upon the stigma, and even in erect and 
fresh flowers, one of the stamens is not. unfrequently seen, still 
covered with pollen, in contact with the stigmatic papille. The 
flowers have a peculiar aromatic smell, which seems the only reason 
for their being visited so much more plentifully than the larger 
flowers of C. sepiwm. , 
Visitors : A. Hymenoptera—Apide : (1) Apis mellifica, L. $, very ab., s. 
and ¢.p.,—to suck, it creeps down into the base of the flower, dusting its head 
and back with pollen, which parts come first in contact with the stigma in each 
flower ; (2) Halictus morio, F. ¢, s., touching neither stigma nor anthers ; (3) 
H. villosulus, K. 2; (4) H. longulus,Sm. 9; (5) H. nitidiusculus, K. 9, all 
three c.p. ; they usually alight on the stigma and then proceed to the anthers, 
thus effecting cross-fertilisation ; (6) Chelostoma campanularum, K. ¢, s., like 
No. 2. B. Diptera—(a) Empide : (7) Empis livida, L., very ab., s., thrusting 
its proboscis into each of the five nectaries one after another ; (6) Syrphide : 
(8) Helophilus floreus, L., s. and fp.; (9) Eristalis arbustorum, L., s. and f.p., 
takes shelter from rain in the flowers ; (10) Syrphus nitidicollis, Mgn. ; (11) 
S. balteatus, Deg. ; (12) Melithreptus scriptus, L. ; (13) M. teeniatus, Mgn., all 
four f.p.,—the large honey-sucking flies effect cross-fertilisation in the same way 
as No. 1, the smaller pollen-feeding flies do so after the manner of Nos. 3—5 ; (ce) 
Muscide : (14) Sepsis, abundant in the passages leading to the honey. ©. Coleo- 
ptera—(a) Nitidulide : (15) Meligethes, do. ; (b) Gidemeride : (16) Gidemera 
virescens, L., fp.; (¢) Cerambycide: (17) Leptura livida, L., feeding on 
pollen, and on the anthers. D. Hemiptera—(18) Nabis, s. Eighteen 
additional visitors are enumerated in No. 590, II. 
Calystegia sepium, R. Br. (Convolvulus sepiwm, L.)—The flowers 
are scentless and without “pathfinders.’ In spite of their large 
size and conspicuous white colour, they are only scantily visited 
by insects. They remain open in rain. On dark evenings (be- 
tween 8 and 10) I have found all the flowers closed, but all open 
on moonlight nights. In other respects the flowers are similar 
to those of Convolvulus arvensis. I have never observed crepus- 
‘cular or nocturnal insects on the flowers, but several of my pupils 
have caught numbers of Sphinw convolvuli upon them in the 
