The Aerating System of Vicia Faba. 
BY 
C. HUNTER, M.Sc. 
With six Figures in the Text. 
HE exchange of gases which is essential for the respiratory activity 
A of each individual living cell of a green plant is carried on by means 
of an intricate system of intercellular spaces, which is continuous throughout 
the plant, and ultimately comes into connexion with the air external to the 
plant by means of stomata and lenticels. De Bary 1 has carefully described 
the different forms of intercellular spaces and the manner in which they 
arise, but the physiological significance of the intercellular spaces of an 
ordinary green plant cannot be said to have received sufficient emphasis. 
The aerating system is quite as important to the plant as the water¬ 
conducting system or the food-conducting system. In order to obtain some 
idea of the complete aerating system of a plant, it was determined to work 
out in detail that of a variety of the Broad Bean— Vicia Faba —which is 
known as the Horse Bean. The plants examined were grown in a mixture 
of fine soil, sand, and leaf-mould. This potting-soil allowed ready access 
of air to the roots, and was also rich in food material. The plants were 
not subjected to any abnormal temperature conditions, as they were grown 
either in a cold frame or else completely in the open air. The results 
obtained for each group of plants were similar, and proved that the 
protection afforded by the cold frame did not affect the structure of the 
different organs. 
The presence of air in intercellular spaces was demonstrated by 
mounting hand-cut sections either in pure glycerine or in glycerine jelly. 
Any air which was present in the sections was rendered visible under the 
microscope, owing to the great difference between the refraction of the rays 
of light by the gas and by the surrounding medium ; and also owing to the 
reflection of the light rays on striking the under surface of the gas. The air 
present in the small intercellular spaces of the sections showed up as dark 
masses, quite distinct from the surrounding cells. This method was 
particularly successful in the case of longitudinal sections. 
1 De Bary : Comparative Anatomy of Phanerogams and Ferns, p. 201 et seq. 
[Annals of Botany, Vol. XXIX. No. CXVI. October, 1915,] 
