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Show 306 PHYSIOGNOMY OF PLANTS. quainted by gardens, descriptions, or herbariums), than there are known insects. According to the average of the statements which I have received from several of our most distinguished entomologists, whom I have had the opportunity of consulting, the number of insects at present described, or contained in collections without being described, may be taken at between 150,000 and 170,000 species. The rich Berlin collection does not contain less than 90,000 species. among which are about 32,000 Coleoptera. A very large number of plants have been collected in distant parts of the globe, without the insects which live on them or near them being brought at the same time. If, however, we limit the estimates of numbers to a single part of the world, and that the one which bas been the best explored in respect to both plants and insects, viz. Europe, we find a very different proportion ; for while we can hardly enumerate between seven and eight thousand European pbrenogamous plants, more than three times that number of European insects are already known. According to the interesting communications of my friend Dohrn, at Stettin, 8700 insects have already been collected from the rich Fauna of that vicinity (and many micro-Lepidopterre are still wanting), while the phrenogamous plants of the same district scarcely exceed 1000. The Insect Fauna of Great Britain is estimated at 11,600 species. Such a preponderance of animal forms need the less surprise us, since large classes of insects subsist solely on animal substances, and others on agamous vegetation (funguses, and even those which are subterranean). Bombyx pini, alone (the spider which infests the Scotch fir, and is the most destructive of all forest insects), is visited, according to Ratzeburg, by thirty-five parasitical Icbneumonides. If these considerations have led us to the proportion borne by the species of plants cultivated in gardens to the entire amount of those which are already either described or preserved in herbariums, we have still to consider the proportion borne by the latter to what we conjecture to be the whole number of forms existing upon the earth at the present time; i. e. to test the assumed minimum of such forms by the relative numbers of species in the different families, therefore, by uncertain multipliers. Such a test, however, gives for the lowest limit or minimum number results so low as to lead us to |