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PASTORAL AND AGRICULTURAL BOTANY 



3. Biennials. The plants of this class expend their energy the first 

 season in forming a root system and foliage leaves. The second year 

 flowers are formed and the seeds are matured. The burdock (A rctium 

 lappa), the sweet clover (Melilotus alba), the wild carrot (Daucus carota), 

 the mullein (Figs. 109 and no), and the teasel belong here. 



4. The fourth class includes the perennial weeds, which perennate 

 by means of roots, rootstocks, bulbs, tubers and other underground per- 

 ennating organs. A number of our noxious weeds are propagated by 

 running, or creeping roots, such as, milkweed (Asclepias cornuti), bindweed 



FIG. in. -Clump of dandelion (Taraxacum ojf.cinale) on a sand lot at Belmar, 

 N. J., June 23, 1919. The clump was one foot high with 213 leaves and 40 head-bearing 

 scapes. 



(Con-volvulus arvensis), sheep sorrel (Rumex Acetosella), Indian hemp 

 (Apocynum cannabinum) and pasture thistle (Cirsium). Many weeds are 

 propagated by subterranean stems or rhizomes. The list includes quack 

 grass (Agropyron repens), poison ivy (Rhus radicans), morning glory 

 (Convolvulus sepium) . 



5. Crown weeds. These have usually a deeply penetrating tap root, 

 which produces shoots around its margin, when cut off close to the ground 

 by a lawn mower, or mowdng machine. The dandelion (Taraxacum 

 officinale, (Fig. in) ribgrass (Plantago lanceolata), curled dock (Rumex 

 crispus) are crownweeds. 



