POLLEN GRAINS AND SEED FERTILISATION. 



23 



selected to bear seeds. Man applies the pollen (magnified at a in Fig. 14), and nature 

 does tlie rest. 



After tlie dust-like pollen is applied to the receptive stigma (^), it actually begins to 

 grow. A thread-like tube is shot out of the pollen grain, in a simihir way to the pro- 

 trusion of the radicle by a germinating seed. This tube forces its way down through 

 the spongy, cellular tissues of the pistil or style, and eventually reaches the ovules, or 

 embryo seeds in the ovary. The point 

 of the pollen tube enters the ovule by 

 a little aperture (e), called the micro- 

 pyle, and some of its contents, or sperm 

 matter, is conveyed to the germ matter 

 in the young ovule, which at once 

 begins to develop as a seed, having a 

 living embryo that holds in itself the 

 united characters of its two parents. 

 But unless this fertilisation is effected, 

 the ovules will wither and die. 



"Double Flowers" have been 

 forced out of their condition by the 

 florist, through an excess of nutriment. 

 The stamens and pistils have been 

 transformed into petaloid segments. 

 That the stamens most usually become 

 changed into petals in our so-called 

 " double " flowers is proved by the fact 



that all our most perfect double flowers ,,.ith two pollen grains growing ; c, ovule being fertilised. 



belong to genera having polyandrous 



or many stamens in the same bloom, such as roses, pteonies, camellias, begonias, 

 buttercups, and malvas. 



When flowers are what is called " perfectly double," both stamens and styles, or 

 pistils, are petaloid, and then no seed is producible ; but it often happens that semi- 

 double flowers are now and then produced, flowers containing one or more perfect 

 ovaries and styles; or one or more perfect stamens bearing fertile pollen, and then, of 

 course, seeds may occasionally be produced. In roses, narcissi, hollyhocks, stocks, 



