32 



been given the credit of refutiug: it. Wolf, in his doctor's thesis on the 

 "Theory of Generation," maintained that the embryo and organs of a phint 

 dfveloi) not by the unfolding of parts already present in miniature, but 

 that they grew out of inidiffereutiated rudiments, the theory of epigenesis. 

 However. Wolfs argimients were far from convincing, as he held that the 

 act of fertilization was merely another form of nutrition. 



Al)out the .same time experiments in hybridization were being carried 

 on by several investigators, and the results obtained supplied much more 

 convincing i)roof against the old theory of evolution. Among the fore- 

 most men in this heltl were Gottlieb Koelreuter and Christian Konrad 

 Sprengel. While Kolreuter brought together many important observations 

 on the sexuality of plants, yet his greatest service consisted in the protluc- 

 tion of hybrids. In this connection it may be of interest to note that his 

 first hybrids were produced between two species of tobacco plants. Xico- 

 tinna puiiicinn and A', rnstica. What he accomplished did not require be- 

 ing changed, but when combined with later observations has been used in 

 the discovery of general principles of hj'bridization. His work seems to 

 belong to our time. Koelreuter showed that only closely allied plants, and 

 not always these, were capable of producing hybrids, and that the mingling 

 of parent;!; characters in the hybrid was the best refutation of the theory 

 of evolution. It was no easy matter to place the proper estimate upon the 

 value of the contributions of this gifted observer. The collectors of the 

 Linnaean school, as well as the true systematists at the close of the IStli 

 century, who wielded a r.owerful infliuence upon botanical thought, had lit- 

 tle understanding for such labors as Koelreuter's. and incorrect ideas of 

 hybrids prevailed in spite of botanical literature. Hybrids were also incon- 

 venient for the believers in the constancy of species. 



Koelreuter's studies were not contined to hybridization alone, for he di- 

 rects attention to the natural way of the transfer of pollen from stamen 

 to stigma, being the first to recognize the agency of insects. He studied 

 pollen grains, showing that fertilization followed pollenation in the ab- 

 sence of light, and rejected the idea that the pollen grain passed bodily 

 into the ovary. With the microscope, howcA-er, he was less skillful than 

 as an experimenter, for he supposed the pollen gr.-iin to be solid tissue, and 

 the fertilizing substance to be oil which adheres to the outside of the grain 

 and finds its way to tlie ovule. The pollen tulie had not been discovered, 

 although the time was one hundred years after the discovery of the cell 

 by Robert Hooke. 



