The Erectness of Plants. 105 



A Further Extension of the Theory. 



An obvious corollary to the theory as outlined above is that 

 the sign of the electric charge on the particles which form the 

 outermost layer of the cytoplasm depends upon the concentration 

 of acids near that membrane. Not only the sign but also the 

 density^ of the charge (i.e., the degree of polarisation or electrifi- 

 cation) will be affected by the varying amounts of acid or alkali 

 present. This corollary forms the basis of the theory of heliotropism 

 outlined above (p. 98). Since the density of the charge on the 

 membrane largely governs the degree of permeability and, there- 

 fore, of turgor and growth, it has very important bearings also 

 upon the influence of the acidity or alkalinity of the medium 

 upon disinfection, plant diseases, infection of plants or animals by 

 fungi or bacteria, the cultivation of bacteria, the long recognised 

 effects of acids and alkalies upon both plants and animals and 

 upon protoplasm in general. The concentration of carbon dioxide 

 governs not only the erectness of plants but also very probably 

 their resistance or susceptibility to disease, their rate of growth, 

 their storage of starch and a multitude of other phenomena in the 

 details of the " living " of these organisms. 



EXPLANATION OF PLATES. 



PLATE I. 



V. — Coated viitli vaseline. UV. — Unvaselined. 



Fig. 1. — Bean seedling showing retardation of growth in the dark with 



seedlings vaselined (V. ) as compared with others left unvaselined 



(U.V.). 

 Fig. 2. — Maize seedlings showing reversal of gravity curvature in one (V.), 



and recoverj' from this effect in another (V^), after being vaselined 



and kept in the dark for several days. 

 Fig. 3. — Vaselined maize seedlings several days after being placed 



horizontalljf in the dark. Three show downward curvature, 



three are erect, and four or five are nearly horizontal. 

 Fig. 4. — Vaselined maize seedlings after similar treatment ; the oiie-which 



is curved down recovered on being placed in sunlight. 



iSee my "Text Book of Botany," foot-note, pp. 353-4. 



