I.

Introduction

Tobacco, plant grown commercially for its leaves and stems, which are rolled into cigars, shredded for use in cigarettes and pipes, processed for chewing, or ground into snuff, a fine powder that is inhaled through the nose. Tobacco is the source of nicotine, an addictive drug that is also the basis for many insecticides (see Smoking).

Tobacco is a member of the nightshade family. There are more than 70 species of tobacco, of which 45 are native to the Americas. The two cultivated species, common tobacco and wild tobacco, are annuals—they live only one growing season. Common tobacco is 1 to 3 m (3 to 10 ft) tall and has a thick, woody stem with few side branches. One plant typically produces 10 to 20 broad leaves that branch alternately from the central stalk. The leaf size depends on the strain. The narrow, trumpet-shaped flowers are dark pink to almost white. Wild tobacco is about 0.6 m (2 ft) tall and has a stem that is more slender and less woody than common tobacco. The leaves have a short stalk that attaches to the stem. The flowers are pale yellow with five separate lobes.