CHAPTER XVI. 



POLLINATION AND FERTILISATION. 



" Pollination " and " Fertilisation " are often used as synonymous 

 terms. This may have been natural when in 1793 Sprengel published 

 his novel observations under the title " The Secret of Nature discovered 

 in the Structure and Fertilisation of Flowers." But at the present 

 day there is little excuse for such laxity. It is well to be clear in the 

 correct meaning of these words when applied to the Higher Flowering 

 Plants. By " pollination " is meant merely the transfer of the pollen 

 from the anther to the receptive surface of the stigma. By " fertilisa- 

 tion " is meant the actual coalescence of two cells: the one is the 

 male gamete derived from the development of the pollen-grain ; the 

 other is the ovum contained within the ovule. Obviously some 

 interval must elapse between the events of pollination and fertiHsa- 

 tion ; it is usually short, but may in extreme cases be as long as a 

 year, or more. Pollination precedes fertilisation in the Flowering 

 Plants and is a means to that end ; hut fertilisation is the end itself. 



The mechanical problem of propagation in Flowering Plants is 

 complicated by the fact that the Plants themselves are immobile. 

 Being rooted in the ground they cannot like the Higher Animals move 

 to seek their mate. The cells that are to carry out fertilisation, viz. the 

 male and female gametes, are produced more or less widely apart from 

 one another. They are themselves incapable of movement, while one 

 of them (the ovum) is deeply embedded in the tissues of the ovule, 

 and covered in by the carpel also. This brings the advantage of 

 protection and nutrition of the germ, but it also greatly complicates 

 the problem of sexual propagation. The steps that are necessary 

 to carry it out are first the transfer of the moveable, though non- 

 motile pollen-grain from the anther to the surface of the stigma of a 

 corresponding plant. That transfer is called Pollination. The second 



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