ADVANTAGES OF KNOWLEDGE OF VEGETABLE PHYSIOLOGY. 185 



lators kept close the atmosphere in the house may be kept at 

 the proper temperature, and it will assist vegetation instead of 

 destroying it. It should be remembered that in every glass- 

 house there is always top ventilation through the laps of the 

 glass, and, generally speaking, I think a one-foot swing ventilator 

 at each end of the house would meet the case, and not give 

 the opportunities of abuse which the present system of top 

 ventilation does. I am sure that many hybrid Orchids, and 

 also many rare species, have departed from this cause alone. 



Once well established, however, the home-raised Orchids 

 have a decided advantage over the imported plants, in that they 

 are much less liable to be affected by our long spells of dull 

 weather and other climatic peculiarities. 



THE ADVANTAGES TO GARDENERS OF SOME 

 KNOWLEDGE OF VEGETABLE PHYSIOLOGY. 



By the Rev. Prof. G. Henslow, M.A., F.R.H.S., V.M.H. 



[Substance of a Lecture delivered at the Society's Gardens, Chiswick, 

 June 15, 1898.] 



Introduction : What is Vegetable Physiology ? — It is 

 the study of the natural history of living plants. 



To secure health in a human being a doctor must understand 

 the structure, functions, and requirements of every organ of the 

 body ; e.g. the lungs are so made as to absorb oxygen from the air 

 for breathing, by which life is kept up ; and one might make a 

 somewhat analogous statement of a leaf — that it is so made as 

 to absorb carbonic acid gas, by which plant structure is built up. 

 Similarly, with regard to the digestive organs, a doctor must 

 know the nature of all the organs of secretion, the relative 

 values of various foods and how they can best secure the growth 

 and development of the body as well as restore its waste. 

 Similarly, to understand how a plant may grow well and thrive 

 it is necessary to know the structure of its organs or members, 

 what they do and what they require. 



Some persons fancy that they can draw a sharp line between 

 practice and science, or between cultivation and physiology, 

 {Such, however, is altogether a mistake ; for all practical 



