THE FLOWERS OF WEEDS. 



35 



subdivided, as in the dissected leaves of yarrow, dog-fennel, etc. 

 The tip of a leaf may be acute or pointed, acuminate or longer 

 pointed, obtuse or dull, emarginaie or notched, etc. Both leaves 

 and stems may be clothed with hairs, as in the corn cockle, or 

 glabrous, without hairs. The hairs, when present, differ greatly in 

 length, stiffness, abundance, etc., in the various weeds. 



The leaves of many weeds bear on the stalk near the base a 

 pair of leaf -like expansions called stipules (Fig. 15, d), which are 

 usually green but often colorless. The margins of sessile leaves 

 may sometimes extend down along the stem as in mullen. Such 

 leaves are said to be decurrcnt and the stem winged. Bracts, scales, 

 glumes, etc.. are only leaves reduced in size which are mainly used 

 to protect the flowers. The seed leaves or cotyledons, are small 



Fig. 9. Illustrating the parts of a flower: a, flower of poppy showing the 4 sets cf floral organs, viz., k, the 

 sepals, together called the calyx; c, the petals, together called the corolla; a, the numerous stamens; g, the 2 pis- 

 ii'.s which contain the ovules. 6, Flower of cinquefoil showing 3 broad sepals, 2 smaller petals alternating with 

 them, a group of stamens, and a large receptacle bearing numerous small pistils, c, Butterfly-shaped flower of 

 sweet pea; d, same spread to show the parts; s, the standard, w, the wings, k, the keel, (After Strasburger and 

 Gray.) 



leaves which exist in all seeds. In some plants, as the squash and 

 beech-nut, they arise above the ground when the seed sprouts. 

 Endogens have but one seed leaf while all exogens have two. 



The flowers of a weed. — The flower is that part of a plant 

 whose chief duty it is to produce seeds or the young of future 

 plants. A complete flower consists of the floral envelope, (Fig. 9,. 

 a), or calyx and corolla, and the essential or sexual organs, the 

 stamens and pistils. If any one of these four divisions of a flower 

 is absent it is said to be incomplete. The calyx or outer floral en- 

 velope is composed of several modified leaves called sepals which 

 are usually green in color, and arranged in a circle so as to cover 

 and protect all the other parts of the flower when in bud. In the 

 corn cockle the lower parts of all 5 sepals have their edges united 

 so a§ to form a tube, while the upper part of each sepal is separate. 



