164 THE FERTILISATION OF FLOWERS. [PART III, 
From the base of the flower rises the ovary ; whose short style 
is terminated by a bi-lobed stigma below the level of the stamens. 
When the anthers dehisce, the stigmatic lobes are still small, and 
probably incapable of fertilisation, but when the stamens wither, 
they are four times as large as at the commencement of flowering 
(Fig. 50). The flowers are thus proterandrous. An insect sucking 
the honey must touch the stamens with one side of its head or 
proboscis, and the stigma with the other; in this case self- 
fertilisation cannot occur, though the stigma and anthers ripen 
at the same time, but cross-fertilisation proceeds regularly. 
Pollen-collecting insects and sometimes even those sucking 
honey, if they thrust their heads several times into the same 
flower, effect self-fertilisation as well as cross-fertilisation. 
The honey on account of its open situation is accessible to 
very various insects, but the flowers are so inconspicuous that they 
are very little visited. Self-fertilisation can take place if needed, 
as the stamens on withering may shed their pollen on the now 
mature stigmas. : 
Visitors: A. Hymenoptera—(a) Apide: (1) Apis mellifica, L. $,s. and 
c.p.; (2) Bombus agrorum, F. 9 §, 8. ; (3) Macropis labiata, Pz. ¢, s. ; (b) 
Vespide: (4) Vespa silvestris, Scop. ab, s.; (5) Eumenes pomiformis, L., s. 
B. Diptera—(6) Culex pipiens, L. ¢,s. 
Lhamnus lanceolatus, Pursh., is dimorphic, according to Darwin, 
but it is not heterostyled in the strict sense (Darwin, 167). 
Rhamnus pumilus, L.—The size of the flower and the number — 
of its parts is reduced in this species, but the plant is visited by 
numerous insects. The flower is generally tetramerous, and the — 
petals exhibit all stages of abortion to complete disappearance 
(609). 
Thamnus catharticus, L., is dina with two sub-forms of each | 
sex (167). 
Orv. SAPINDACEZ. 
Serjania cuspidata, St. Hil—The flower resembles the labiate 
type, and, lke Paullinia, L., and Cardiospermum, L., is 
proterandrous. 
Many species of Acer, according to Delpino, are proterandrous 
and are fertilised by flies (178, 360). 
87. AiscuLus Hippocastanum, L.—The arrangement of the 
flower was thoroughly described by Sprengel. My own notes and 
