50 TEXTBOOK OF ZOOLOGY 



the nature and appearance microscopically of several organs of the 

 body; Grew had made rather extensive microscopic studies of plants, 

 and in 1831 Kobert Brown had discovered the nucleus of the cell, 

 but not until the work of Schleiden in 1838 and Schwann in 1839 

 was the cell theory formally enunciated. The former a botanist and 



Fig. 17. — Matthias J. Schleiden (1804-1881), noted German botanist who helped 

 establish the cell theory. (From Locy, Growth of Biology, published by Henry 

 Holt and Company, Inc.) 



the latter a zoologist, each working independently, came to the same 

 conclusion and in 1839 collaborated their ideas. This theory, as 

 they gave it, was in substance, All living things (plants and animals) 

 are composed of cells. 



