326 ‘ PHARMACEUTICAL BOTANY 
through the study of the comparative embryology and structure 
of plant organs. He later published his famous Prodromus which 
was continued by his son Alphonse de Candolle with the aid of 
eminent collaborators. This work gives descriptions of genera 
and species of Dicotyledons and represents a modification and 
elaboration on the system of Jussieu. 
From 1862 to 1883, George Bentham and Joseph D. Hooker, 
two eminent British botanists, issued their Genera Plantarum. 
This work contains a systematic arrangement of the Phanerogams 
with a description of all of the genera then known. 
This system was followed by the systems of A. W. Eichler 
(Berlin 1883) and of Engler and Prantl. The latter, called ‘‘Die 
naturlichen Pflanzenfamilien,” has since its appearance become the 
most popular guide of systematists. It is based on the belief that 
the absence of a perianth is a primitive condition and that 
Monocotyledons precede Dicotyledons. 
In 1926, J. Hutchinson, of the Royal Botanical Gardens at 
Kew, issued the first volume of his work, ‘‘ The Families of Flower- 
ing Plants.” ‘This is a new natural system on the seed plants and 
is based on the assumption that plants with sepals and petals 
associated with other floral and anatomical characters regarded 
as primitive are more ancient than plants without sepals or 
petals. The Monocotyledons are placed after the Dicotyledons 
from which they are claimed to have been derived. 
In every modern natural system, every individual belongs to 
a species or unit of classification. 
A SpPEctEs is a mental concept of a group of individual plants 
having their more stable characters in common. While the 
individual plants making up the group called a species may differ 
in the size and number of their various organs and even show small 
differences in the shape of their leaves or fruits, the parts of their 
flowers will usually be quite similar in form, number and arrange- 
‘ment. These more stable characters enable one to recognize 
any members of a given species and to distinguish it from mem- 
bers of other species. When an individual of a species repro- 
duces, its offspring will show the same essential or more stable 
characters as its parent or parents. Thus, all the Oak trees 
which we commonly recognize as white oak constitute the species 
Quercus alba, 
