A FEW OBSERVATIONS ON THE PHYSIOLOGY OF PLANTS. 99 



viating many of the diseases of life. To the botanist, their admirable 

 arrangement and affinity of principles or qualities afford interesting 

 and useful information ; and to the horticulturist the structure of 

 plants, and every circumstance affecting their growth, claims his 

 especial regard. But at the same time that its importance is admitted, 

 it must be acknowledged to be surrounded with difficulties, for it in- 

 volves the question of the peculiar functions of living beings, a ques- 

 tion which, notwithstanding the numerous valuable discoveries that 

 different philosophers, from age to age, have made concerning it, 

 still, in a great measure, remains unanswered. Chemistry, it is true, 

 has of late done much to elucidate the nature of vegetable growth, 

 but we are still ignorant of the peculiar controlling effects of vitality 

 of chemical action ; nor, on the other hand, are we better informed 

 as to the precise manner in which light, heat, and electricity, influence 

 vital action, and consequently the growth of plants. A knowledge of 

 these points would enable the horticulturist to carry on his operations 

 with almost uniformly successful results, but in the absence of such 

 knowledge, he must at present be content to pursue the course which 

 experience, and the amount of science already made available, shall 

 point out ; and it is gratifying to be aware of the fact, that though we, 

 have not a full knowledge of all the circumstances affecting the growth 

 of plants, we do know enough to admit of valuable practical applica- 

 tion. While, therefore, we reduce our science to practice, let us 

 endeavour to extend its bounds, adhering to no theory which is not 

 based on substantial facts, at the same time remembering that, with 

 the advance of science, theories which to-day appeared well founded 

 have shortly given way to others, which, upon the discovery of some 

 fact previously unknown, have, in their turn, shared the fate of their 

 predecessors. Admitting, as I freely do, the value of theories, without 

 which science would lose the greater part of its value, I would simply 

 caution your readers against their abuse : to have recourse to theories 

 is very beneficial, yet to be entirely guided by them, in matters where 

 our knowledge is not precise and certain, is voluntarily to give up all 

 hope of advancement in the path of knowledge. 



The material conditions necessary to healthy vegetation are a suitable 

 soil, sufficiency of water, and atmospheric air. Plants being properly 

 placed, with regard to these circumstances, and duly acted on by light, 

 heat, and electricity, are observed to vegetate vigorously. The soil 



i 2 



