Angiospermous Plants — Flowering Plants 213 



prominent ridge above the hilum, the raphe (ra'fe) (Gr. raphe, seam), 

 which is formed by the ovule beneath; (3) the micro pyle below the hilum 

 (mi'kropile) (Gr. mikros, small; pyle, gate) which is a small opening 

 in the seed coat for the entrance of pollen; (4) seed coats which form 

 the protective covering; (5) two cotyledons (kot i -le' don) (Gr. kotyle, 

 cup) which are the two fleshy halves of the bean for the storage of food; 

 (6) the plumule (or epicotyl) with its true leaves folded over the grow- 

 ing tip; (7) the hypocotyl; and (8) the radicle (rad'ikel) (L. radix, 

 root) which is continuous with the hypocotyl and forms the embryonic 

 root. The tip of the radicle points toward the micropyle. All of these 

 structures may best be seen in seeds which have been soaked to initiate 

 germination. 



During germination^ the food of the cotyledons is digested and trans- 

 ferred to the plumule, hypocotyl, and radicle. The embryonic, primary 

 root is formed from the radicle which bends downward under the influ- 

 ence of gravity. The hypocotyl elongates and carries with it the plumule 

 and the two cotyledons out of the soil. The two cotyledons spread to 

 allow the developing foliage leaves of the plumule to develop. The 

 cotyledons may develop chlorophyll for carrying on photosynthesis for 

 a time, but eventually they shrivel. The roots absorb water and nutrients 

 from the soil and conduct them to the stalk (stem) . 



SUNFLOWER 



Helianthus (he li -an' thus) (Gr. helios, sun; anthos, flower). — The 

 sunflower belongs to the phylum Tracheophyta; subphylum Pteropsida; 

 class Angiospermae; subclass Dicotyledoneae; family Compositae (kom- 

 poz'ite) (L. cum, together; ponere, to place) because of the many 

 closely compacted individual flowers (florets) which form a head, com- 

 monly mistaken for the flower (Fig. 57-). Common plants with com- 

 posite flowers include sunflowers, dandelions, ragweeds, cockleburs, gold- 

 enrods, daisies, asters, zinnias, dahlias, marigolds, lettuce, artichoke, etc. 

 The enormous production of seeds and the efficient devices for their 

 dispersal have distributed them widely. The pollen of many of them, 

 including goldenrods, ragweeds, etc., are causes of pollen (hay) fever. 



A sunflower plant consists of a stem with nodes (joints), at which 

 leaves are borne, and inter nodes, between successive nodes, by which 

 growth occurs by an elongation process. 



Internally, a mature stem of a dicotyledonous plant such as a sun- 

 flower (Fig. 57) consists of (1) a central, pith region composed of thin- 



