Hippocrates described 234 species, Theophrastus followed with 500. Pliny knew, as well as can be made out now, 800. Tonmefort, at the beginning of the last century, described 10,146. Many of these had to be united as not distinct enough for modern science, till at the death of Linnaeus 7,294 had been described. De Candolle, in the Theory of Elementary Botany, made 30,000 named species. Lindley, in 1853, gave the number as 92,920. Now, in the neighborhood of 150,000 species are known, with possibly an equal number not yet known. Thus figures the Revue de l'horticulture Beige.

The Relation of Heat to the Sexes of Flowers was discussed before the Philadelphia Academy of Natural Sciences last year, as noted at the time in these columns, and the important principle developed that it takes less heat to bring forth a male flower, or the male parts of a flower, than it does in the case of the female. This explanation is being found the key to much that was supposed to be among the "unknowables" before. In Europe, or at least, the northern portion of it, where the winter temperature is low till the spring actually arrives, the male flowers, or organs of plants, remain inactive till the weather is warm enough to bring forward the females also, when they receive the necessary pollination requisite for fruitfulness. In other countries, where there are occasionally warm days or warm periods, the male flowers in monoecious or diaecious plants are brought forward to maturity, while the females, desiring a still warmer temperature, linger behind. As a result, some trees, like hazelnuts and walnuts, which produce regularly crops of nuts in some countries, become barren in others. In our own country it was shown, in the items which have been already given, that the hazelnut or filbert often fails in this country, for this reason.

It now appears that the same law operates on the production of walnuts in California. Mr. Gillett, of Nevada City, has recently-written an essay on this subject, showing that the climate of that State advances the male flowers, while the females remain quiescent. The male catkins are all overblown and have fallen long before the female flowers have been brought forward; and, hence, they are usually barren. In order to secure successful walnut culture in California, they have introduced a variety called the Juglans prae-parturiens, which requires, both for the male and female flowers, a higher temperature before the flowers push. In other words, the variety blooms later. With this they have great success. - Independent.

How the knowledge of plants has progressed of late years may be illustrated by that curious family Orchideae. Linnaeus could count all his genera on his fingers; now Bentham and Hooker in their recent work describe 334. - Independent.