YOUNG OF HIGHER PLANTS 



103 



or twice, and two or more of 

 these nuclei pass down the 

 tube and reach the tissues in 

 the ovary. In the meantime 

 the nucleus of the large spore 

 in the ovary has divided 

 into eight or more nuclei, 

 and one of these becomes the 

 nucleus of an egg. The 

 nuclei in the pollen tube es- 

 cape and one of them unites 

 with the egg nucleus. In this 

 way fertilization takes place. 

 Thus we see that pollen 

 grains are not sperms, but 

 nuclei in the pollen tube after 

 the pollen has germinated are 

 really the sperms. The egg 

 is not formed directly by the 

 growth of the ovary tissues, 

 but by the division of the 

 nuclei in the large spore 

 which the ovary produced. 



4. What is the Real Differ- 

 ence Between the Old and 

 New Views? In the old view 

 we have just a straight, di- 

 rect union of a male cell pro- 

 duced by a plant (such as an 

 apple tree) with a female cell 

 produced by the same apple 

 blossom. In the new view 

 we have the flower producing 

 spores as in the fern, only in 

 the flower we have two kinds 

 of spores: a small spore pro- 



Fisnre 25. Diagrammatic view 

 of a pistil, showing entering pollen 

 tubes. One of them has reached 

 the tissue which contains the egg, 

 and fertilization is about to occur. 

 From Coulter's Plant Life and 

 Plant Uses. 



