OF PLANTS. 251 



knows something, just because his weak eyes can reach no 

 farther than the book, from which he has so laboriously 

 collected his crumb of wisdom. 



In former Lectures have at least been touched upon, the 

 chief points on which depend the Life of Plants, their variety 

 on the globe, and consequently the variety of vegetation. 

 The explicable life of the Plant is, formation of organic 

 matter out of inorganic compounds. The plant is there- 

 fore dependant on the condition of the soil, in the widest 

 sense of the word, on the store of nutriment it contains, 

 and on all that influences the chemical process of formation, 

 consequently, above all, upon a determinate temperature. 

 Now that I have, in the foregoing paragraphs, treated of 

 the conditions of temperature, I will here briefly consider 

 more minutely the influence of the soil. Usually two very 

 different so-called stations of plants have been distinguished, 

 but they have never been, properly speaking, defined 

 according to physiological principles. The universal, indis- 

 pensible nutrient substance of plants, and, at the same 

 time, the matter by means of which all the rest are con- 

 veyed into it, is water. Without water there is no vegeta- 

 tion. This element of the ancients presents itself to the 

 plant in three different forms, and according to these must 

 we, above all things, discriminate the stations of plants. 

 The Orchidaceous plants of the tropical forest let their 

 peculiarly constructed roots hang down from the branch to 

 which they cling, in the moist, warm atmosphere, and 

 absorb water in the form of vapour. Our Water-lilies and 

 the proper bog-plants will only flourish when surrounded 

 by liquid water, or, at least, with their roots dipping in it. 

 The case is quite different with the great majority of 

 plants ; they have to extract their nutriment from the 

 earth, which contains the moisture to be absorbed into 



