Angiospermous Plants — Flowering Plants 211 



forms the primary root of the seedling, (5) a sheathlike coleoptile (kol' e- 

 op til) (Gr. koleos, sheath; ptilon, feather) which completely encloses the 

 plumule, (6) a sheathlike fo/^or/izza (kol e o -ri' za) (Gr. A;o/^oi^, sheath; 

 rhiza, root) which encloses the radicle. 



Upon germination the radicle breaks through the coleorhiza and forms 

 a temporary primary root. Adventitious, fibrous roots are soon formed. 

 The plumule breaks through the protective coleoptile to form true leaves 

 which develop chlorophyll for photosynthesis. 



GARDEN BEAN 



Phaseolus (fa -se' o lus) (L. fabaceous, bean) (Figs. 55 and 56) . — The 

 common garden bean belongs to the phylum Tracheophyta; subphylum 

 Pteropsida, class Angiospermae, the subclass Dicotyledoneae; family 

 Leguminosae (le gum i -no' se) (L. legumen, to gather) because the 

 legumes (fruits) are frequently gathered for various purposes. The 

 family is commonly called the pea or pulse family (L. puis, pottage or 

 porridge) and includes such foods as peas, beans, peanuts, lentils, etc., 

 such forage crops as clovers, alfalfa, vetches, etc., and such ornamental 

 plants as sweet peas, lupine, lotus, wistaria, Judas tree, etc. Locust trees 

 are used as timber. The family includes such drug plants as senna, lico- 

 rice, etc. Leguminous plants add nitrogenous materials to the soils 

 through the fixation of free nitrogen by the actions of special types of 

 bacteria which inhabit the enlarged nodules on the roots. 



The bean plant may be short, bushlike, or a vinelike annual, depend- 

 ing upon the variety. The stalks (stems) may be long and slender and, 

 due to unequal rates of growth on opposite sides, have a tendency to 

 twine spirally around objects with which they come in contact. The 

 external epidermis is rather thin and affords limited protection. In cer- 

 tain parts of the stems and leaves there niay be hairs (outgrowths of epi- 

 dermal cells) . 



The leaves of the bean plant are usually trifoliate (three leaves arising 

 from one point) and net veined (frequently branched). The thin epi- 

 dermal layer contains stomata for the exchange of gases. Guard cells 

 control the size of the opening of the stoma. Below the stomata are air 

 spaces surrounded by cells which contain chlorophyll in green chloro- 

 plasts. The chlorophyll, through energy supplied by light, combines the 

 carbon dioxide and water to form carbohydrates by the process of photo- 

 synthesis. Part of the manufactured foods may be used by the plant 

 and the remainder stored, particularly in the developing seeds. The 



