A HISTORY OF SCIENCE 



Stages of formation of the grains of pollen, the evolution 

 of which is so remarkable in tradascantia. 



" The few indications of the presence of this nucleus, 

 or areola, that I have hitherto met with in the publica- 

 tions of botanists are chiefly in some figures of epi- 

 dermis, in the recent works of Meyen and Purkinje, 

 and in one case, in M. Adolphe Broigniart's memoir on 

 the structure of leaves. But so little importance seems 

 to be attached to it that the appearance is not always 

 referred to in the explanations of the figures in which 

 it is represented. Mr. Bauer, however, who has also 

 figured it in the utriculi of the stigma of Bletia Tanker- 

 villicz has more particularly noticed it, and seems to 

 consider it as only visible after impregnation." 2 



SCHLEIDEN AND SCHWANN AND THE CELL THEORY 



That this newly recognized structure must be im- 

 portant in the economy of the cell was recognized by 

 Brown himself, and by the celebrated German Meyen, 

 who dealt with it in his work on vegetable physiology, 

 published not long afterwards ; but it remained for an- 

 other German, the professor of botany in the Univer- 

 sity of Jena, Dr. M. J. Schleiden, to bring the nucleus 

 to popular attention, and to assert its all-importance 

 in the economy of the cell. 



Schleiden freely acknowledged his indebtedness to 

 Brown for first knowledge of the nucleus, but he soon 

 carried his studies of that structure far beyond those of 

 its discoverer. He came to believe that the nucleus is 

 really the most important portion of the cell, in that it 

 is the original structure from which the remainder of 

 the cell is developed. Hence he named it the cytoblast. 



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