THE STORY OF NINETEENTH-CENTURY SCIENCE 



the days of the earliest lenses. It had been noticed, 

 too, by here and there an observer, that certain of the 

 solid tissues seemed to present something of a granular 

 texture, as if they too, in their ultimate constitution, 

 were made up of particles. And now, as better and bet- 

 ter lenses were constructed, this idea gained ground 

 constantly, though for a time no one saw its full signif- 

 icance. In the case of vegetable tissues, indeed, the fact 

 that little particles encased in a membranous covering, 

 and called cells, are the ultimate visible units of struct- 

 ure had long been known. 

 But it was supposed that 

 animal tissues differed radi- 

 cally from this construction. 

 The elementary particles of 

 vegetables " were regarded 

 to a certain extent as indi- 

 viduals which composed the 



MATTHIAS JAK01! SCHLEIDEX 



entire plant, while, on the 

 other hand, no such view 

 was taken of the elementary 

 parts of animals." 



In the year 1833 a further 

 insight into the nature of the 

 ultimate particles of plants 

 was gained through the ob- 

 servation of the English microscopist Robert Brown, 

 who, in the course of his microscopic studies of the epi- 

 dermis of orchids, discovered in the cells "an opaque 

 spot," which he named the nucleus. Doubtless the same 

 "spot" had been seen often enough before by other ob- 

 servers, but Brown was the first to recognize it as a 

 component part of the vegetable cell, and to give it 



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