which a plant
requires to maintain it in a flourishing condition we must ascertain
within what limits its period of vegetation, may vary, and what
quantity of heat it requires. This most remarkable circumstance was
first observed by Boussingault, but unfortunately we do not as yet
possess sufficiently accurate accounts of the conditions of culture in
the various regions of the earth, to enable us to follow out this
ingenious view in all its details. His theory is, that the time
required by a plant to arrive at maturity is as the inverse ratio of
the temperature; therefore, knowing the mean temperature of any place,
and the number of days which a plant takes to ripen, the time required
at any other point more or less elevated, can easily be ascertained.
Peter Purry, a native of Switzerland, who settled in Charleston in
the eighteenth century, in a memorial to the Duke of Newcastle, then
Secretary of State, sets out with this postulate, that "there is a
certain latitude on our globe, so happily tempered between the
extremes of heat and cold, as to be more particularly adapted than any
other for certain rich productions of the earth; among which are silk,
cotton, indigo," &c.--and he fixes on the latitude of 33 deg., whether
north or south, as the one of that peculiar character.

The following Table, showing the climate, duration and production of
certain plants cultivated in tropical America, is from the proceedings
of the Agricultural Society of Grenada. The second, column gives the
altitude in English yards above the level of the sea. The third, the
mean temperature by Fahrenheit's thermometer. The fourth, the average
time required to commence bearing. The fifth, the number of plants in
a Spanish "fanegada" of 170 varras, about 153 square yards. The sixth,
the average duration of each plant. The seventh, the average produce
of each plant in the year:--

-----------------+-----------+---------+--------+------+------+--------
| 2 | 3 | 4 | 5 | 6 | 7
|Level of |Mn. Temp.| Time |No. of| |Average
|the Sea, to|Deg. Min.|Required|plants|Years |produce
-----------------+-----------+---------+--------+------+------+--------
Cacao | }|81.17 |61/2 | 1,156| 40 |11/4 lb
(_Theobroma |587 yds. }|46.00 |yrs | | |per tree
Cacao_) | }| | | |