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 in- 

 sects 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 has 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 be- 

 tween seven and eight thousand European phsenogamous 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-Lepidopterae are still 

 wanting), while the phaenogamous 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 Ichneumohides. 



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 



