. Pharmaceutical botany. Botany; Botany, Medical. 30 PHARMACEUTICAL BOTANY Branched hairs can be seen upon the leaves of the common field weed, Mullein. Geranium and the Stinging nettle afford examples of glandular hairs. Plant hairs are adapted to many different purposes. They absorb nourishment in the form of moisture and mineral matter in solution. Those which serve as a protection to the plant may be barbed and silicified, rendering them unfit for animal food, or, as in the nettle, charged with an irritating fluid, penetrating the skin when touched, injecting the poison into the wound. A d
. Pharmaceutical botany. Botany; Botany, Medical. 30 PHARMACEUTICAL BOTANY Branched hairs can be seen upon the leaves of the common field weed, Mullein. Geranium and the Stinging nettle afford examples of glandular hairs. Plant hairs are adapted to many different purposes. They absorb nourishment in the form of moisture and mineral matter in solution. Those which serve as a protection to the plant may be barbed and silicified, rendering them unfit for animal food, or, as in the nettle, charged with an irritating fluid, penetrating the skin when touched, injecting the poison into the wound. A dense covering of hairs also prevents the ravages of insects and the clogging of the stomata by an accumulation of dust. They fill an important in the dispersion of seeds and fruits, as with their aid such seeds as those of the milkweed are read- ily scattered by the wind. The reproductive organs of many Cryp- togams are modified hairs, as the sporangia of The Leaf Fig. 24. — Different forms of epidermal out- growths. I, Hooked hair from Phaseolus multiflorus; 2, dimbing hair from stem of Humulus Lupulus; 3, rod- like wax coating from the stem of Saccharum ofiSci- narum; 4, climbing hair of Loasa hispida; 5, stinging hair of Urtica urens. (Fig. 3 after de Bary; the remainder from Haberlandt.) Leaves (folia) are stem appendages which have their origin just back of the apex of the stem, are regularly arranged upon it, and con- sist of expansions of its tissues. The functions of a leaf are photosynthesis, assimilation, respiration and transpiration. The most essential function of plants is the conversion of inorganic into organic matter; this takes place ordinarily in the green parts, containing chlorophyll, and in these when exposed to sunlight. Foliage is an adaptation for increasing the extent of green surface. The leaf when complete consists of three parts, lamina, petiole, and STIPULES. The lamina or blade is the expansion of the stem into a more or less deli
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