ANNOTATIONS AND ADDITIONS. 119 



nean) . 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 

 Ichneumonides. 



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 pro- 

 portion 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, there- 

 fore, by uncertain multipliers. Such a test, however, gives 

 for the lowest limit or minimum number results so low as 

 to lead us to perceive that even in the great families, our 

 knowledge of which has been of late most strikingly en- 

 riched by the descriptions of botanists, we are still 

 acquainted with only a small part of existing plants. 

 The Repertorium of Walpers completes Decandolle's Pro- 

 dromus of 1825, up to 1846 : we find in it, in the family 

 of Leguminosse, 8068 species. We may assume the ratio, 

 or relative numerical proportion of this family to all phse- 

 nogamous plants, to be -^V as we find it ~$ within 

 the tropics, -^ in the middle temperate, and -^ in the 

 cold northern zone. The described Leguminosee would 

 thus lead us to assume only 169400 existing phsenogamous 

 species on the whole surface of the earth, whereas, as we 

 have shewn, the Compositse indicate more than 160000 

 already known species. The discordance is instructive, and 



