490 



ON THE GEOGRAPHY OF PLANTS. 



wonderful when we find that Stedman and his soldiers were forced to 

 sleep with their heads thrust into holes made in the earth with their 

 bayonets, in order to escape from their tormenting bites; while Baron 

 Humboldt tells us, the wretched inhabitants are accustomed to stretch 

 themselves on the ground and pass the night buried in the sand three 

 or four inches deep. 



2. Similium pertinax, Kollar ; in Brazilian, Boraxudo ; in Portu- 

 guese, Mosquilto. The colour is black, the wings translucent, the 

 antennae and the legs pale yellow, the shanks {tibiae) of the hind legs 

 and all the feet (tarsi) blackish. The body is one twelfth of an inch 

 in length. The wings in some lights have a reddish gloss, and are 

 exceedingly thin and furnished with delicate wing ribs. The poisers 

 (halleres) are yellow. The female, as in the former instance is the 

 most troublesome, and the blood flows copiously from the wound she 

 inflicts. This, which is about the size of a pin's head, ought to be 

 squeezed firmly to expel the insect poison. 



Our authors report that there are many other species of Similium 

 in Brazil, which are similarly troublesome. They add that the Brazi- 

 lians call every species of troublesome fly Mosquilto. 

 Lee, Kent, )th Oct. 1833. 



- ON THE GEOGRAPHY OF PLANTS. 



BY BARON HUMBOLDT. 



The numerical relations of the forms of vegetation are capable of being 

 investigated in two very different modes. Supposing that the natural families 

 of plants are studied without reference to their geographical distribution, 

 the question will arise as to which form of organisation it is after which the 

 greatest number of species have been created. Are there most Glumacea? or 

 Composita; in the world? Do these two tribes together constitue a fourth part 

 of phoenogamous vegetation ? What proportion is borne by monocotyledon es to 

 dicotyledones ? Questions of this kind refer rather to the science of vegetable 

 organisation and of mutual affinities. But if, instead of studying natural 

 groups of species in this abstract manner, we view them with reference to the 

 relations they bear to climate or to the distribution over the surface of the globe, 

 other questions of a more varied nature will arise. Which families, for instance, 

 are more predominent in the torrid zone than in the polar circle? Are Compo- 

 site more numerous in the same parallel of latitude or in the same isothermal 

 line in the old world or the new ? Do those forms, which are found to diminish 

 in retreating from the equator to the pole, follow a similar law of decrement in 

 rising from the plains into the mountains of the equator ? Do the proportions 



