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 



