312 
JAMES GEERE DICKSON 
characteristic constant modifications are shown. The plants grown 
in the culture solutions deficient in magnesium develop numerous broad 
leaves, which are at first very bright green but when older show marked 
striping as the chlorophyll between the veins disappears. 
The plants grown in the culture solutions deficient in calcium 
develop numerous dark green leaves nearly as long as those of the 
plants growing in the magnesium-deficient solutions. The lower 
leaves, however, soon show an inrolling of the margin, a characteristic 
which Loew (1899) and Tottingham (1914) ascribe to a high mag- 
nesium-calcium ratio. Later, at about the time of flowering, brown 
spots appear upon these inrolled leaves and finally the affected leaves 
dry and become twisted about the stem. Schimper (1890) describes 
brown spots on the leaves of Tradescantia grown in the absence of 
calcium, and von Portheim (1901) notes the appearance of similar 
spots on the leaves of beans grown in calcium-deficient soils. 
The plants grown in the culture solutions deficient in potassium 
have a smaller total leaf surface than those grown in the normal solu- 
tions, but their leaves have very thick dark green laminae. During 
the period of blossoming, the lower leaves of these plants show long, 
irregular dark-brown blotches, which appear first near the leaf-base 
and gradually extend towards the apex. 
The plants grown in the culture solutions deficient in phosphorus 
develop a slender culm which bears a few dwarfed, fleshy leaves. 
Both the leaves and stems are purplish green, with the purple color 
apparently gradually replacing the green in the older tissues of the 
plant. The abnormal coloring appears to be brought about by the 
presence in the reticulum of the chloroplast of a purple colloidal 
substance intermixed with the chlorophyll, and resulting perhaps 
from a progressive decomposition of the latter. Russell (1913) has 
shown that when barley is grown in phosphorus-free solutions the 
stems become reddish near the apex. 
The plants grown in the solutions weak in nitrogen produce on an 
average four narrow, yellowish gieen leaves. Upon microscopic ex- 
amination, the chloroplasts of these leaves appear to be more or less 
disorganized. 
The period of development is shortened by fully a week when 
nitrogen or phosphorus is limited, but a deficiency in magnesium 
or in calcium increases the period of growth about ten days beyond that 
of the plants grown in the normal solutions. 
