248 BIOLOGY AND ITS MAKERS 



and was published in Miillcr's Archiv, in 1838, under the 

 German lillc of Ueber Phytogenesis. As stated above, the 

 cell had been recognized for some years, but the question of 

 its origin had not been investigated. Schleiden says : " I may 

 omit all historical introduction, for, so far as I am acquainted, 

 no direct obsers'ations exist at present upon the development 

 of the cells of plants." 



He then soes on to define his view of the nucleus fcvto- 

 blast) and of the development of the cell around it, saying: 

 '' As soon as the cytoblasts have attained their full size, a 

 delicate transparent vesicle arises upon their surface. This 

 is the young cell." As to the position of the nucleus in the 

 fully developed cell, he is very explicit: "It is evident," he 

 says, "' from the foregoing that the cytoblast can never lie 

 free in the interior of the cell, but is always enclosed in the 

 cell-wall," etc. 



Schleiden fastened these errors upon the cell-theory, since 

 Schwann relied upon his observ^ations. On another point of 

 prime importance Schleiden was WTong: he regarded all new 

 cell-formation as the formation of ''cells within cells," as dis- 

 tinguished from cell-division, as we now know it to take place. 



Schleiden made no attempt to elaborate his views into a 

 comprehensive cell-theory, and therefore his connection as 

 a co-founder of this great generalization is chiefly in paving 

 the way and giving the suggestion to Schwann, which enabled 

 the latter to establish the theory. Schleiden's paper occupies 

 some thirty-two pages, and is illustrated by tw^o plates. He 

 was thirty-four years old when this paper was published, and 

 directly afterward was called to the post of adjunct professor 

 of botany in the University of Jena, a position which with 

 promotion to the full professorship he occupied for twenty- 

 three vears. 



Schwann's Treatise. — In 1838, Schwann also announced 

 his cell-theory in a concise form in a German scientific period- 



