HISTORICAL SKETCH 13 



of its functions must be governed to a considerable extent by the organ- 

 ism as a whole (Wager). Such divergence of opinion led to much dis- 

 cussion over the question of organic individuality, which remains as 

 one of the important problems of modern biology. 



But in spite of all these changes we should not forget the great service 

 rendered by Schleiden and Schwann in the formulation of the Cell Theory. 

 Huxley (1853) estimated the value of their contribution in the following 

 lines : 



"Doubtless the truer a theory is the more appropriate the colligating 

 conception the better will it serve its mnemonic purpose, but its absolute 

 truth is neither necessary to its usefulness, nor indeed in any way cognizable by 

 the human faculties. Now it appears to us that Schwann and Schleiden have 

 performed precisely this service to the biological sciences. At a time when the 

 researches of innumerable guideless investigators, called into existence by the 

 tempting facilities offered by the improvement of microscopes, threatened to 

 swamp science in minutiae, and to render the noble calling of the physiologist 

 identical with that of the 'putter-up' of preparations, they stepped forward with 

 the cell theory as a colligation of the facts. To the investigator, they afforded 

 a clear basis and a starting point for his inquiries; for the student, they grouped 

 immense masses of details in a clear and perspicuous manner. Let us not be 

 ungrateful for what they brought. If not absolutely true, it was the truest 

 thing that had been done in biology for half a century." 



Fertilization and Embryogeny. In Plants. Although it was known 

 to the ancients that there is in plants something analogous to the sexual 

 reproduction seen in animals, ideas of the organs and processes involved 

 were very vague. Like Grew and others in the seventeenth century, the 

 botanists of antiquity were aware of the fact that the pollen in some way 

 influences the development of the ovary into a fruit with seeds. Definite 

 proof that the stamens are (to speak somewhat loosely) the male organs 

 was furnished in the well-known experiments of R. J. Camerarius (1691). 

 But in spite of the excellent work of J. G. Koelreuter (1761), C. K. 

 Sprengel (1793), and K. F. Gaertner (1849), all of whom proved the 

 correctness of this conclusion, the idea of sexuality in plants was vigor- 

 ously combatted in certain quarters for many years. 



An important step in advance was made when G. B. Amici (1830) 

 followed the growth of the pollen tube from the pollen grain on the stigma 

 down to the ovule. Schleiden (1837) and Schacht (1850,1858) took up 

 the study and made a curious misinterpretation: they regarded the ovule 

 as merely a place of incubation for the end of the pollen tube, which they 

 supposed to enter the ovule and enlarge to form the embryo directly. 

 The work of Amici (1842), Tulasne (1849), and others showed the falsity 

 of this notion, but an acrimonious discussion raged about the subject 

 for a number of years, Schleiden (1842, 1844) using the most vigorous 

 language in support of his position. After Hofmeister (1849) had fol- 



