248 BIOLOGY AND ITS MAKERS 



and was published in M tiller's Archiv, in 1838, under th 

 German title of Ueber Phylogenesis. As stated above, th 

 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 



