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Show 300 PHYSIOGNOMY OF PLANTS. different systems of vegetation, what harvest may still remain to be reaped in the several families. The comparison of the numerical ratios of families in different already well-explored zones, has conducted me to the recognition of laws according to which, in proceeding from the Equator to the Poles, the vegetable forms constituting a natural family decrease or increase as compared with the whole mass of phanerogamre belonging to each zone. We have here to regard not only the direction of the change (whether an increase or a decrease), but also its rapidity or measure. We see the denominator of the fraction which expresses the ratio increase or decrease: let us take as our example the beautiful family of Leguminosre, which decreases in going from the equinoctial zone towards the North Pole. If we find its proportion or ratio for the torrid zone (from 0° to 10° of latitude) at 1~, we obtain for the part of the temperate zone which is between 45° and 52° latitude -{-y;, and for the frigid zone (lat. 67" to 70°) only :lr The direction followed by the great family of Leguminosre (increase on approaching the Equator), is also that of the Rubiacere, the Euphorbiacere, and especially the Malvacere. On the contrary, the Grasses and Juncacere (the latter still more than the former) diminish in approaching the Equator, as do also the Ericere and Amentacere. The Compositre, Labiatre, Umbelliferre, and Cruciferre, decrease in proceeding from the temperate zone, either towards the Pole or towards the Equator, the Umbelliferre and Cruciferre decreasing most rapidly in the last-named direction; while at the same time in the temperate zone the Cruciferre are three times more numerous in Europe than in the United States of North America. On reaching Greenland, the Labiatre have entirely disappeared with the exception of one, aud the Umbelliferre with the exception of two species; the entire number of phamogamous species, still amounting, according to Hornemann, to 315 species. It must be remarked at the same time that the development of plants of different families, and the distribution of vegetable forms, do not depend exclusively on geographical, or ev-en on isothermal latitude; the quotients are not always on the same isothermal line in the temperate zone, for example, in the plains of North America and those of the Old Continent. Within the tropics there is a very |