CHAPTER VII 



FERTILIZATION 



In various ways the male gametophyte reaches the stigma. 

 The literature dealing with pollination has become very exten- 

 sive, and can not even be recapitulated here, especially as it is 

 an ecological subject. The development of tubes from pollen- 

 grains lodged upon stigmas has long been known, but the rela- 

 tion of the tubes to fertilization was long misunderstood. An 

 historical account of the early views of fertilization among An- 

 giosperms, together with the citation of literature, was given 

 by Schacht 1 in 1850, and by Hofmeister 2 in 1851. A few 

 notes from Schacht's account may not be without interest, and 

 the reproduction of some of his figures will serve to show the 

 technique of the time and to illustrate how theories may in- 

 fluence interpretation (Fig. 65). 



In 1681 Malpighi discovered the ovule and the embryo- 

 sac, and also examined the pollen, but regarded it as a useless 

 secretion. Xo important advance was made until 1823, when 

 Amici discovered the pollen-tube on the stigma of a Portula'ca 

 and succeeded in tracing the tube to the ovule. In 1826 Bron- 

 gniart traced the pollen-tube in many plants, and in Pepo 

 macrocarpus saw hanging from the micropyle the end of the 

 tube that had passed into the embryo-sac ; " but," says Schacht, 

 " he misinterpreted the phenomenon, for he regarded the pol- 

 len-tube as a fertilizing tube through which the fertilizing con- 

 tents were brought to the embryo-sac, there to be taken up by 

 the ' embryonal vesicle,' a cell arising in the sac." In 1836 

 Robert Brown described the development of the integuments, 

 and later traced the pollen-tubes of orchids and asclepiads from 

 the stigma to the micropyle. In 1833 the knowledge of the 

 subject may be summarized as follows: there had been observed 



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