Physiology of Plants. 79 



done on the theory of fertilization or amphimixis, on the 

 theory of development, and on the theory of species. 

 Worthy of mention along with Kcelreuter were J. and 

 K. F. Gartner, father and son, who continued experi- 

 ments on similar lines. 



Christian Konrad Sprengel (1750-1816), who loved 

 botany too well to be a successful rector of Spandau, 

 may be said to link Camerarius to Darwin. rgn 

 In his Newly Discovered Secret of Nature in 

 the Structure and Fertilization of Flowers, he expounded 

 and illustrated three remarkable conclusions: (i) that 

 many of the characteristics of flowers nectaries, mark- 

 ings, shapes, &c., are to be interpreted as adaptations 

 in relation to the insect visitors which secure fertiliza- 

 tion or pollination ; (2) that cross-fertilization is the rule, 

 not the exception, there being not a few reasons why 

 it is unlikely, if not impossible, that carpels are pollin- 

 ated by pollen from the stamens of the same flower; 

 and (3) that a large number of flowers are dichogamous, 

 i.e. with stamens and carpels ripening at different times, 

 one of the ways in which self-fertilization is prevented. 

 Subsequent experiments by Andrew Knight, by William 

 Herbert (1837), and especially by K. F. Gartner (1844), 

 disclosed the fact which Sprengel had missed, that 

 cross-fertilization has better results than self-fertiliza- 

 tion as regards the number and vigour of the seeds, a 

 conclusion which Darwin was not slow to use in sup- 

 port of his theory, that the adaptations ensuring cross- 

 fertilization were the outcome of a process of natural 

 selection. 



Pollination is the process by which the pollen is trans- 

 ferred by insects, or by the wind, or otherwise, from the 

 stamens to the stigma. There, stimulated The Act of 

 by a sugary secretion, the pollen-grain sends Fertilization. 

 out a tube, the pollen-tube, which grows down the style, 

 and enters the micropyle of the ovule within which the 

 ovum or egg-cell lies. The mingling of elements from 

 the pollen-tube with the ovum is the real act of fertiliza- 

 tion, and the first steps in making this clear were taken 

 by Amici. In 1823 he first saw the pollen-tube emerge 

 from the pollen-grain, and by persevering observation 



