290 THE HISTORY OF 



multiformity appear to lie in the richness of the soil in 

 readily soluble inorganic matters, which in the first place 

 give rise to a variation in the chemical processes of the plant, 

 and thus to a greater or less deviation in the form.* These 

 two conditions meet in the tropics, because they are 

 dependant one upon the other, since the more luxuriant 

 vegetation called forth by the moist, warm atmosphere, 

 prepares by its death and rapid decay, a soil richer in soluble 

 inorganic matters, for the succeeding generation. Similar con- 

 ditions, that is to say, greater richness in soluble inorganic 

 matter, are exhibited on our manured cultivated lands, and 

 the Alpine regions, which are continually supplied with an 

 abundance of soluble matter from the naked higher rocks 

 more exposed to the action of the weather.f We know, 

 moreover, that varieties once formed, when they have con- 

 tinued to vegetate under the same conditions for several 

 generations, pass into sub-species, that is into varieties 

 which may be propagated with certainty by their seeds, as 

 for instance, our beds of Peas, our Cabbage plantations 

 and our Wheat-fields testify. How then if the same 



* See the Seventh Lecture. 



t No one who casts a glance over an accurately investigated Flora, 

 can deny that the Alpine plants exhibit a greater richness in form, 

 and series of most striking varieties. It is not so evident in regard 

 to the cultivated land, and I will therefore offer the following brief 

 remarks ; among the German families of plants, the Goosefoots and 

 Oraches (Chenopodea and Atriplicecs) most especially grow on 

 rubbish, heaps of compost, and in gardens, therefore peculiarly 

 under the inevitable influence of the conditions given by our culti- 

 vation ; and no collector is ignorant of the abundance of forms and 

 varieties which most of these plants deviate into. If we select 

 from the best and most carefully revised Flora of Germany, those 

 genera which exhibit the most stable species, and at the same time 

 include some species which vegetate in quite a different way under 

 the influences of our cultivation, it at once becomes evident that 



