CHAP, i.] Joseph G. Koelreuter and Konmd Sprengel. 411 



burst and allowed the contents to escape. But he explained 

 the pollen-tube, which he had thus seen, incorrectly by sup- 

 posing that these projections were intended to prevent the 

 bursting of moistened grains. It was not till sixty or seventy 

 years later that the matter was fully understood. Koelreuter 

 supposed the contents of the pollen-grain to be a 'cellular 

 tissue,' and the true fertilising substance to be the oil which 

 adheres to the outside of the grains, but is formed inside them 

 and finds its way out through fine passages in the coat. The 

 bursting of the pollen-grains, which his opponent Gleichen 

 thought must take place to allow of the escape of his supposed 

 spermatozoids, seemed to him an unnatural proceeding. 



Starting from the hypothesis, that the oil which clings to 

 the pollen-grains is the fertilising substance, Koelreuter pro- 

 pounds his view of the process of fertilisation in accordance 

 with the chemical notions of the day ; he first rejects the 

 idea that the pollen-grains themselves can reach the ovary, 

 and then says : ' Both the male seed and the female moisture 

 on the stigmas are of an oily nature, and therefore when they 

 come together enter into a most intimate union with one 

 another, and form a substance which, if fertilisation is to ensue, 

 must be absorbed by the stigma and conveyed through the 

 style to the so-called ovules or unfertilised germs.' Koelreuter 

 therefore made the fertilisation really take place on the stigma, 

 the mingled male and female substance making its way into the 

 ovary and there producing the embryos in the seed. He had 

 expressed this view before in 1761; he repeated it in 1763 

 with the idea that the male and female moistures unite together, 

 as an acid and an alkali unite to form a neutral salt ; a new 

 living organism is the result at once or later of this union. 

 In an investigation which he made in 1775 into the conditions 

 of pollination in Asclepiadeae he reverted to this idea, and 

 insisted that the act of fertilisation in the whole vegetable and 

 animal kingdom is a mingling of two fluids. But at a later 

 period he seems to have no longer considered the moisture 



