2 4 2 PLANT AND ORGANIC CHEMISTRY 
Iron is found to be essential to green plants only. If a seed¬ 
ling be cultivated by water culture in a fluid containing no iron, 
the leaves will become pale until at length they are nearly white, 
but on the addition of a small quantity of iron to the solution, 
or if the white leaves are painted with a dilute iron solution, 
they will very shortly become green. It plays an important part 
in the formation of the green coloring-matter, though it does 
not enter into its chemical composition. 
“Buckwheat, 1 barley, and oats do not flourish when grown 
in solutions containing no chlorides, and as in these plants the 
chlorophyll corpuscles become overfilled with starch grains, it 
was thought that this element was of importance in connection 
with the translocation of carbohydrates.” 
Sodium 2 has been used in water culture to replace potassium, 
but the plants deprived of potash did not develop. 
Manganese is abundant in the ash of Trapa natans. I also 
found it in the different portions of Yucca angustijolia . 3 
Iodine and bromine are found in marine Algce. and in minute 
quantity in some plants grown far from the sea. 
Silica is found in the form of soluble or insoluble silicic acid. 
It occurs principally in the cell wall, but it has been found in the 
cell sap of a plant (Equisetum hiemale 4 ), and certain cells in 
the pseudo-bulbs of epiphytic orchids 5 contain each a plate of 
silica. 
Experiments have shown that the absorption of silicic 6 acid 
greatly assists the assimilation of other plant foods, and that 
plants to which it is supplied show a decidedly more healthy 
development of grain and straw than others not so treated. 
Silica is doubtless of mechanical use, giving firmness and rigid¬ 
ity to plant tissues; though the real cause of “laying” of crops 
1 Vines, Cambridge edition, p. 136. Also, Beyer, Landw. Versuchs-Stat., xi. 
Leydhecker, ibid., viii. 
2 Salm-Horstmar, Knop and Schreber. 
3 “Yucca Angustifolia,” Helen C. De S. Abbott, Trans. Am. Philos. Soc., 
Dec. 18, 1885, also ante, p. 126. 
4 Lange, Ber. d. Deutsch. Chem. Ges., xi. 
8 Pfitzer, Flora, 1877. 
6 C. Kreuzhage and E. Wolff, Landw. Versuchs-Stat., xxx, 161-198 {Jour. 
Chem. Soc., 1884, p. 1112). 
