248 BIOLOGY AND ITS MAKERS 



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

 German title of Ueber Phylogenesis. 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 observations exist at present upon the development 

 of the cells of plants." 



He then goes on to define his view of the nucleus (cyto- 

 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 observations. On another point of 

 prime importance Schleiden was wrong: 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 two 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 years. 



Schwann's Treatise. In 1838, Schwann also announced 

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



