248 BIOLOGY AND ITS MAKERS 
and was published in Miiller’s Archiv, in 1838, under the 
German title 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 J 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- 
