PLATE 10 
Longitudinal section of a stem of Ricinus communis injected July 18,1916, witli dis¬ 
tilled water containing 10 per cent malic acid. Photographed on July 28. X9. 
There is a copious proliferation from the outer pith cells filling the pith cavity. 
Malic acid in small amounts is a normal constituent of the plant cell. 
