160 SELECTIONS FROM ADDRESSES. 



that have been gained, and the present aspect and prospects of 

 agricultural science. 



Whoever examines the internal structure of plants, even cur- 

 sorily, will be struck with its analogy to that of animals. He 

 will find in both, organs for the reception of food, for its di- 

 gestion and assimilation, as well as a system of circulation and 

 reproduction. The plant, indeed, has its peculiarities of or- 

 ganization, as for instance, that no nervous system has been dis- 

 covered in it; and yet it seems possessed of irritability, if not 

 sensibility. Under the microscope, however, it is a wonderful 

 structure; and notwithstanding all the difficulties of the in- 

 vestigation, the patience of physiological botanists has disclosed 

 an organization in plants almost as wonderful as that of animals. 

 The manner in which the sap ascends, is, indeed, still involved 

 in some obscurity ; though the curious property possessed by 

 vegetable and animal tissues, of causing fluids of different 

 densities to pass through them, sometimes inwardly and some- 

 times outwardly, technically called endosmosis and exoa?nosis, 

 is, doubtless, the predominant agency concerned in a process so 

 adverse to gravity. 



To the chemist it has long been manifest, that the true way 

 to ascertain what food is needed by plants, is to analyze their 

 whole substance, to see what ingredients they contain. For 

 the notion prevalent not long since, that vegetables have the 

 power to transmute one simple substance into another, is utterly 

 exploded ; and no scientific man now expects to find in plants 

 any ingredient that, does not exist in the soil or the atmosphere. 

 The uniform result of careful and repeated analysis of plants 

 is, that they are mainly and essentially composed of foijr prin- 

 ciples, viz. : carbon, oxygen, hydrogen, and nitrogen. These 

 are combined together in various ways, and form the almost 

 entire mass of vegetables. But when plants are burnt, they 

 leave a solid residuum, or ash, which often contains eight or 

 nine other simple substances; viz., chlorine, iodine, sulphur, 

 phosphorus, potassium, sodium, calcium, magnesium, alumin- 

 ium, silica, iron, and manganese. These are the inorganic in- 

 gredients; and though essential to the composition of plants, 

 they do not always exist in the same proportions, even in the 



