42 PRESENT-DAY GARDENING 
CROSS-FERTILISATION 
The flowers of Rhododendrons are simple in structure. 
The calyx is five-lobed, the size of the lobes varying in 
the different species, being in some cases almost leaf-like. 
The corolla is usually bell- or funnel-shaped, with five or 
more lobes. There are, as a rule, ten stamens, sometimes 
five (Azalea), and they have long, hairy filaments and oblong, 
two-celled anthers which open at the top. The pollen grains 
are very small, and are held together by a spider’s-web-like 
substance, termed viscin, so that when they are touched by 
an insect or other agency, the whole mass is drawn out, 
and hangs together. The style is club-shaped ; the stigma 
is flat-headed, and it is sticky when in a receptive condition. 
Rhododendrons are protandrous, that is, the pollen is 
ready before the stigma. To prevent self-fertilisation, there- 
fore, it is necessary to remove the anthers before they are 
ripe. In nature the flowers are fertilised by insects attracted 
by the honey secreted at the base of the corolla, and in 
their efforts to reach it their bodies become smeared with 
the pollen, which is then conveyed to another flower ; the 
stigma is situated so that it must come in contact with the 
pollen adhering to the insect's body, and thus pollination 
is effected. If the conditions are favourable the pollen 
immediately begins to swell and develop a unicellular 
protoplasmic filament, called the pollen tube, which grows 
down the style until it comes into contact with the ovule or 
oosphere and fertilises it. The flower then fades, the ovary 
(seed-vessel) remaining and increasing in size until, at 
maturity, it turns brown and bursts open to allow the seeds 
to escape. The seeds are very small, a single capsule if 
properly fertilised containing several thousands. From the 
