THE ROOT 87 
the stele. The pith is in the centre. Cambium provides 
for inerease in thickness. 
Types.—Tap root, adventitious, napiform, conical, 
fusiform, tuberous, prop-roots, air roots. 
Chemical Constituents of plants.—Carbohydrates— 
starch, sugar, cellulose, inulin; proteins. Plants con- 
tain the elements C, O, H, N, 8S, phosphorus, potassium, 
caleclum, magnesium iron, silicon, and chlorine—all, 
except carbon, obtained from the soil. 
Soil contains minerals, humus, water, bacteria 
and air. 
Mechanical analysis may be made by means of 
sieves to separate the soil grains into groups according 
to their size. 
Classification_Sandy soil # sand; Clay soil ? clay; 
Loam, half sand and half clay; Calcareous soil, 4 
stone; Peat, excessive humus. 
Root-acid is chiefly carbonic acid formed by the 
carbon dioxide of respiration uniting with water. Other 
acids are also present. These acids dissolve minerals. 
Soil water may be gravitational, capillary or 
hygroscopie. 
Nitrogen.—Green plants get N from the soil as 
nitrates derived from humus. The bean family is 
assisted by bacteria. Parasites get it from the host, 
and Carnivorous plants by digesting animals. Water 
cultures show the relative importance of the different 
plant foods. 
QUESTIONS ON CHAPTER IIT. 
1. State what you consider the twelve chief facts about 
roots. 
2. Compare the roots of a grass with the root of a seedling 
tree. 
3. Define tap-root, adventitious roots. 
