292 
HISTORY OF BOTANY. 
solution ; the green parts of vegetables were observed to exhale 
oxygen in the light, and carbonic acid gas in the dark ; and the 
carbon left by the decomposition of the carbonic acid, was 
shown to be incorporated into the vegetable substance, giving to 
the wood its strength and hardness. 
Bernard de Jussieu proposed a method of classing plants ac- 
cording to certain distinctions in the seed, which were found to 
be universal ; this method was perfected and published by his 
nephew, Antoine-Laurent de Jussieu, and is now universally re- 
ceived as the best mode of natural classification which has yet 
been discovered. — We call this method natural, because it aims 
to bring into groups such genera of plants as resemble each 
other in medicinal and other properties, while the system of 
Linnaeus is called artificial, because by a certain rule, plants are 
brought into groups which have no such resemblance in their 
properties. We therefore find in one of the Linnaean classes, 
the poisonous flag and the nutritious grass, the grain which 
supports life and the darnel which destroys it ; in another the 
healthful potatoe and the poison mandrake, the deadly hemlock 
and the grateful coriander. We might thus go through this 
system and constantly meet with similar contrasts in the quali- 
ties of the plants which are here collected into the same classes, 
nor are their external appearances less unlike ; for here the ole- 
ander and pigweed, the tulip and the dock meet in the same 
classes. This system it should always be remembered, is not 
the whole science of botany, but is the key to the natural meth- 
od, by which alone we should find great difficulty in ascertain- 
ing the names of plants ; it is, as it were, a stepping stone by 
which we must ascend to the valuable knowledge which cannot 
well be reached in any other way. The more practical a bota- 
nist becomes, the less need he has for this assistance ; the eye 
becomes quick to seize on natural characters without reference 
to the dictionary, as the artificial system is aptly termed. Thus 
a pupil in studying a language may in time be able in a degree 
to dispense with his dictionary ; but he could never have pro- 
ceeded thus far without its assistance. For more particular ex- 
planations of Jussieu’s method, you are referred to the compari- 
son of that with the method of Linnaeus and Tournefort in the 
remarks on classification. 
Adanson, previous to the time of the younger Jussieu, had 
published a system of classification, in which he arranged plants 
according to the resemblance observed in all their organs. In 
one class all which had similar roots were placed ; in another 
all which had similar stems ; a third was arranged by resem- 
Jussieu’s classification. 
