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 oflS.ce 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 Ferns. 



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 delicate framework, made up of the branching vessels 

 of the petiole. 



The petiole is the leaf stalk. The stipules are leaf-like appendages 

 appearing at the base of the petiole. 



