HISTORICAL SKETCH 7 



During the first third of the nineteenth century no name is of greater 

 interest to cytologists than that of Robert Brown (1773-1858). Al- 

 though he is famous chiefly for his great taxonomic monographs and his 

 morphological work, he is known in cytology as the man who is usually 

 given the credit for the discovery of the nucleus, which he announced 

 in 1831. Although it was Brown who was impressed by the probable 

 importance of the nucleus, and who concluded in 1833 that it is a normal 

 cell element, certain other observers, notably Fontana, who described a 

 nucleus in 1781, and Meyen, who saw it in Spirogyra in 1826, should 

 share the honor for its discovery. The phenomenon which has since 

 been known as "Brownian movement" was seen by Brown in 1827. 



The first period in the development of our subject is seen to have 

 been one in which there was a tendency to indulge in speculation to an 

 extent quite unwarranted by the facts at hand. As we have already 

 pointed out, however, this speculation was of considerable importance to 

 us, in that it had to do with questions which later became central prob- 

 lems of cytology. Carefully made observations were meanwhile in- 

 creasing in number and varieyt, and the time eventually became ripe 

 for the formulation of a theory which would correlate these data and give 

 a definite trend to cytological investigations. Such a theory was soon 

 forthcoming. 



The Foundation of the Cell Theory. The year 1838 marks an epoch 

 in the history of biology. In this and the following year Schleiden and 

 Schwann founded the Cell Theory, which, in view of its enormous in- 

 fluence upon all branches of biological science, may be regarded as second 

 in importance only to the Theory of Evolution. We have seen that cells 

 had been observed by various workers during many years, and had been 

 recognized as being constantly present in the bodies of living organisms, 

 but it remained for Schleiden and especially Schwann to formulate a 

 comprehensive theory embracing the known facts and affording a start- 

 ing point for further researches. 



The Cell Theory stated primarily that the body is composed entirely of 

 cells and their products, the cell being the unit of structure and function 

 and the primary agent of organization. Subsidiary to this was Schleiden's 

 theory of cell-formation, which should not be confused with the main 

 thesis just stated. 



Matthias Jakob Schleiden (1804-1881) is one of the most prominent 

 and interesting characters in botanical history. He studied law at 

 Heidelberg, medicine at Gottingen, and botany at Berlin, where he met 

 Schwann and Robert Brown. The association of these men undoubtedly 

 meant much to the future of botany and zoology. Eventually Schleiden 

 became Professor of Botany at Jena, where he remained for 23 years. 

 Schleiden was famous not merely because of his own work, but chiefly as 

 the result of the tremendous impetus which he gave to investigation. 



