chap, i.] Investigation of the fertilisation-process. 433 



followed the pollen-tubes into the ovary, but also observed 

 that one finds its way into the micropyle of each ovule. 



Thus the question was suddenly brought near to its solution, 

 when observers began to wander from the right path in 

 different directions. Robert Brown showed in 1831 and 1833 

 that the grains in the pollen-masses of Orchids and Asclepiads 

 put forth pollen-tubes as in other plants, and that fine tubes 

 are found in the ovary of Orchids in which pollination has 

 taken place ; but he was in doubt about the connection of 

 these tubes with the pollen-grains, and rather inclined to think- 

 that they were formed in the ovary, though possibly in con- 

 sequence of the pollination of the stigma. Schleiden went 

 wrong in a very different way, and by so doing made the 

 question as prominent in botanical research, as was that of the 

 origin of cells at this time. He published in 1837 some ex- 

 cellent investigations into the origin and development of the 

 ovule before fertilisation, certainly the best and most thorough 

 of the day. He at the same time showed that Brongniart's 

 and Brown's doubts were unfounded, and confirmed the state- 

 ment of Amici, that the pollen-tubes make their way from the 

 stigma to the ovule, which they enter through the micropyle. 

 But he made them push forward a little too far, for he asserted 

 positively that 'the pollen-tube pushes the membrane of the 

 embryo-sac before it, making an indentation, and its extremity 

 then appears to lie in the embryo-sac. The extremity of the 

 tube now swells out into a round or oval shape, and cell-tissue 

 forms from its contents ; the lateral organs, one or two coty- 

 ledons, are then produced, the original apical point remaining 

 more or less free and forming the plumule. The portion of 

 the tube underneath the embryo and the fold of the embryo 

 sac which envelopes it are divided off sooner or later and dis 

 appear, so that the embryo now really lies in the embryo-sac' 

 This view, which appears to rest on direct observation and is 

 illustrated by figures which answer to the description, corre- 

 sponds with the old theory of evolution and has a striking 



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