43 2 History of the Sexual Theory. [BOOK in. 



wards through the style to the ovules, and are there either 

 hatched into embryos or assist in their production. This way 

 of conceiving the matter was closely connected with the theory 

 of evolution which then prevailed, and seemed to find some 

 countenance in the seed-corpuscles of animals ; it was also 

 supported by the observation that pollen-grains placed under 

 the microscope in water often burst and discharge their con- 

 tents in the form of a granular mucilage. It has been already 

 mentioned that Koelreuter rejected this view ; he declared the 

 bursting of the pollen-grains to be contrary to nature, and con- 

 sidered the oil which exudes from the grains to be the fertilising 

 substance. This view was adopted by Joseph Gartner and 

 Sprengel, but it fell into disesteem, while that of Needham and 

 Gleichen commanded some assent some years longer. The 

 next question was, how the granular contents of the pollen- 

 grain reach the ovules. Accident supplied a starting-point for 

 further consideration. Amici, who was examining the hairs on 

 the stigma of Portulaca for another purpose, saw on that 

 occasion (1823) the pollen-tube emerge from the pollen-grain, 

 and the granular contents of the latter, commonly known as 

 the fovilla, execute streaming movements like the well-known 

 movement in Chara. The desire to verify this remarkable 

 fact, and to discover how the fertilising substance is absorbed 

 by the stigma, led Brongniart in 1826 to examine a great 

 number of pollinated stigmas. He succeeded in establishing 

 the fact that the formation of pollen-tubes is a very frequent 

 occurrence. The want of perseverance in following out his 

 observation and a prepossession in favour of Needham's old 

 theory prevented him from discovering the course of the 

 pollen-tubes all the way to the ovules ; he supposed, indeed, 

 that after penetrating into the stigma they open and discharge 

 their granular contents, and he maintained distinctly that these 

 are analogous to the spermatozoids in animals, and are the 

 active part of the pollen. But now Amici addressed himself 

 more earnestly to the question, and in 1830 he not only 



