BAR, SCHLEIDEN, UNGER. 109 
I must next mention Carl Ernst Bar, the great reformer of 
animal embryology. Ina lecture delivered in 1834, entitled 
“The Most General Laws of Nature in All Development,” 
he shows, in the clearest way, that only in a very childish 
view of nature could organic species be regarded as perma- 
nent and unchangeable types, and that really they can be 
only passing series of generations, which have developed by 
transformation from a common original form. The same 
conception again received firm support from Baer, in 1859, 
through a consideration of the of laws the geographical 
distribution of organisms. 
J. M. Schleiden, who founded, thirty years ago, in Jena, a 
new epoch in Botany by his strictly empirico-philosophical 
and truly scientific method, illustrated the philosophical 
significance of the conception of organic species in his inci- 
sive “Outlines of Scientific Botany,”’’ and showed that it 
had only a subjective origin in the general law of specifica- 
tion. The different species of plants are only the specified 
productions of the formative tendencies of plants, which arise 
from the various combinations of the fundamental forces of 
organic matter. 
The eminent botanist, F. Unger, of Vienna, was led by 
his profound and comprehensive investigations on extinct 
vegetable species, to a paleeontological history of the de- 
velopment of the vegetable kingdom, which distinctly asserts 
the principle of the Theory of Descent. In his “ Attempt at 
a History of the World of Plants” (1852), he maintains the 
derivation of all different species of plants from a few 
primary forms, and perhaps from a single original plant, a 
simple vegetable cell. He shows that this view is founded 
on the genetic connection of all vegetable forms, and is 
