42 HISTORY OF PHYTOPATHOLOGY 



these forms. Zoologic investigations 1 had established 

 the facts of heteromorphism among insects, notably in 

 the case of aphids. The true relation of gall wasps, tape- 

 worms, and other parasitic animals to their hosts was 

 becoming increasingly clear to scientific workers. 



Nevertheless, the deep-rooted theory of spontaneous 

 generation still dominated to a great extent the doctrines 

 on reproduction. Accumulating evidence against it 

 and a growing understanding of the significance of this 

 evidence were of themselves powerless to overcome the 

 handicap which centuries of established acceptation 

 gave to the prevailing dogma. The overthrow of this 

 ancient superstition awaited the magic power of master 

 minds. The middle of the nineteenth century saw their 

 entrance upon the scientific stage. The brilliant re- 

 searches and convincing demonstrations of that noted 

 French savant, Louis Pasteur, 2 swept away the nebu- 

 lous foundations of spontaneous generation. Kiichen- 



1 For classic works on this subject see 



Steenstrup, Johann Japetus Smith: Om Fortplantning og Udvikling 

 gjennem vexlende Generationsvrikker en saeregen Form for Opfostringen 

 i de lavere Dyrklassen, pp. I-IV + 1-76, Kjobenhavn, 1842. A German 

 translation by Lorenzen appeared in 1842 and from this an English trans- 

 lation by Rusk in 1845 under the title: On the alternation of generation; 

 or the propagation and development of animals through alternate 

 generations. 



Owen, Richard: On parthenogenesis or the successive production of 

 procreating individuals from a single ovum, pp. 1-76, London, 1849. 



Siebold, Carl Theodor Ernst von: On a true parthenogenesis in 

 moths and bees; a contribution to the history of reproduction in animals. 

 Translated from the German by William L. Lallas, pp. I-VIII + 1-110, 

 1857. The original appeared in 1856. 



2 Frankland, P., and Frankland, Mrs. P.: Pasteur, pp. 1-224, Xew 

 York, 1898. See especially ch. 5, and Vallery-Radot's, The Life of 

 Pasteur, in two volumes, 1902, vol. 1, ch. 5. 



