DR. SCHLEIDEN'S THEORY OF AGRICULTURE. 31 



Without further preface, we proceed with our account of the 

 argument. 



There is a great difference between experience and observa- 

 tion ; the latter merely indicates the external relation of one 

 phenomenon with another as regards space and time ; the former 

 their intimate connection in point of cause and effect. Without 

 experience in this true sense of the word there can be no theory. 

 "What is meant therefore in the present volume by Theorj'^ of 

 Agricultvire is only the apposition of those sciences which can 

 alone place an intelligent cultivator in a condition to make real 

 and useful experiments, and when a sufficient quantity of these 

 are collected, and not till then, a theory of agriculture in the 

 real sense of the phrase will be possible. At present we must be 

 content by means of chemical and physical science to make agri- 

 cultural experience possible. 



The first question which arises is what are cultivated plants 

 or plants of husbandr}', and in what respect do they differ from 

 wild plants. It is quite self-evident that all laws to which wild 

 plants are subject, hold good of cultivated plants so long as their 

 inapplicability is not proved by intrinsic difference of nature. 

 The greater part of writers on agriculture are wholly incom- 

 petent to say whether cultivated plants are under more or less 

 favourable circumstances than wild plants. The first thing 

 which strikes us about those plants whose cultivation is carried 

 on on a large scale is that they comprise a very small portion of 

 the species which are distributed over the earth. Out of the ten 

 thousand species of grasses scarcely twenty species are exten- 

 sively cultivated ; of the immense family of Papilionaceous 

 plants, perhaps twelve ; half a dozen Crucifers ; scarce as many 

 Umbellifers, Chenopods, and 8olanads : besides a sprinkling of 

 species cultivated in tlie tropics with which we are less familiarly 

 acquainted. 



Out of 300 families, consisting of some 200,000 species, we 

 have mentioned nearly all that come within our present scope. 



These plants may be divided into two different groups ; those 

 of which we do not know witli certainty the wild state, and those 

 whose origin is well ascertained. The most important cereals 

 for instance, as Indian Corn, Rice, Wheat, Rye, Oats, and 

 Barley, are never met with truly wild. All the researches of 

 travellers in America after the wild state of the Indian Corn 

 have been vain, and our European species which are supposed to 

 have been derived from the East have never been found in coun- 

 tries except where it was more than probable that tiiey had been 

 introduced by the hand of man. The wild originals seem to 

 have perished before what are called the historical ages. Nor 

 indeed do they establish themselves in general as wild plants ; 



