Planetary spaces, temperature of, xxxii, 1; xxxiv, 57.
Planorbis, see [Zoology, Mollusca.]
[Plants,] number of known species, xlix, 172.
— of New York, number of indigenous, J. Torrey, xl, 77.
—, classification of, according to a natural system, Robert Brown, i, 435.
—, grand division, into exogens, endogens and acrogens, xxxii, 295.
—, other subdivisions, xxxii, 296, 299.
—, soul or spiritual life of, C. F. P. von Martius, xl, 170.
—, ammonia disengaged by growing, x, 190.
—, carbonic acid disengaged by the roots of, xlv, 227.