INTRODUCTION. IX 



matter first becomes endowed with life. It is there that we 

 meet with its earliest, humblest indications. We know that 

 every plant is formed out of the mineral matter of the earth 

 and atmosphere, and that the vegetable world is formed out of 

 mineral matter for the support of animal life. Thus the plant 

 connects the animal with the mineral. He who would suc- 

 cessfully study the laws of life as developed in the animal 

 world certainly ought not to neglect the investigation of plants 

 on which animals depend for food, or rather for their very 

 existence. 



It must be clear, to reflecting minds, that plants and animals 

 exercise a great many of the functions of life in common. 

 Both are nourished by food and air, are subjected to disease, 

 decay, and death, and have the power of self-reproduction, or 

 of continuing their species. Plants appear to be subject to 

 similar organic laws to animals, in the development of their 

 tissues, and the life in them is probably only a modification of 

 the same universal principle of action which pervades all or- 

 ganic being. In the prosecution of physiological researches, it 

 is therefore of the utmost importance that we should become 

 conversant with the phenomena of vegetable vitality. In the 

 development of living nature, there is too evident a system of 

 dependency, and no link in the great chain of being can be 

 dispensed with. Human physiology will progress, and the 

 noble art of healing be better understood, in proportion as we 

 understand the expression of life in inferior organic forms. If 

 we would understand the higher manifestations of life in our- 

 eelves, we must neglect the study of nothing that has life, 



