560 
APPENDIX. 
Page 351. 
According to Payen ( Comptes rendus, viii. 60.), those manures 
are the most efficient which are richest in nitrogen, for he considers 
that plants are generally able to obtain, in most cultivated soils, a 
sufficient supply of the other principles necessary to their exist- 
ence, without the addition of manure. But this does not quite 
agree with an assertion of Boussingault, that although some plants 
rob the air of a considerable quantity of nitrogen, yet others do not 
assimilate it at all. (/5. 55.) 
Page 380. 
Mr. Rigg has investigated the connection between nitrogen and 
plants, the results of his enquiries being given in the Philosophical 
Transactions for 1838, p. 395. &c. He finds the youngest parts 
of plants richest in nitrogen, the germ of Peas and Beans con- 
taining by weight about 200 parts of that gas for 1000 parts of 
carbon, while the cotyledons contain only from about 100 to 140 
parts. He is disposed to believe that those seeds of the same 
kind, which contain the largest quantity of nitrogen, germinate the 
earliest. Alburnum he finds to contain more nitrogen than duramen, 
and fast-growing timber more than slow-growing, whence he infers 
that nitrogen exercises its influence in causing decomposition. The 
latter opinions he considers to be rendered still more probable by 
the proportion of nitrogen found in different species of wood, cceteris 
paribus: thus in satin wood and Malabar teak, both timber of great 
durability, the quantity of nitrogen is almost inappreciable ; in 
Dantzic and English oak, the quantity is also very small ; in 
American birch which soon decomposes, nitrogen is found in large 
quantities. Mr. Rigg finds nitrogen in large quantities in Vine 
leaves when they first make their appearance: as they are developed 
it decreases in proportional quantity ; is in excess during the period 
of most rapid growth, and towards the close of the year it is com- 
paratively small. He states the full-blown petals of the Rose to 
contain 24 parts of nitrogen in 1000 of carbon, while the unex- 
panded and central petals contain 66 parts. 
In another paper also published in the Philosophical Transactions 
for 1838, p. 403., Mr. Rigg has considered the evolution of 
nitrogen during the growth of plants, and the sources from 
which they derive that element. He states that his enquiries all 
tend to prove that nitrogen is evolved during the healthy perform- 
ance of the functions of plants ; that the proportion which it bears 
