33° 



TEXTBOOK OF BOTANY 



an abundant production o'f seeds to insure their perpetuation 

 and spread ; and some of our annual weeds are remarkable 

 for the vast numbers of flowers, fruits, and 

 seeds that they bear. A striking example of 

 this sort is the common ragweed, abundant 

 along roadsides and in neglected fields. The 

 ragweed is a composite. Other weeds of the 

 same family which Ukewise bear seeds in great 

 abundance are the mayweed, cocklebur, horse- 

 weed, and prickly lettuce. The grass family, 

 too, contributes a number of troublesome 

 annual weeds, among them chess, wild oats, 

 squirrel-tail grass, pigeon grass, crab grass, and 

 bur grass. The dodders and the wild morning- 

 glory are representatives of the convolvulus 

 family ; the buffalo bur and the jimson weed 

 of the nightshade family ; the lamb's quarters 

 and the Russian thistle of the goosefoot family ; 

 and the wild mustard and French-weed (penny 

 cress) of the cress family.- The pigweed, purs- 

 lane, smartweed, and chickweed are also 

 common and widespread. 



350. Biennial Weeds.— 

 This group is a compara- 

 tively small one. It is 

 plain that, like annuals, 

 biennials must depend 

 chiefly upon seeds for their 

 perpetuation and increase. The com- 

 posite family, whose members have such 

 effective means of producing;- and scatter- 

 ing their seeds, contributes a few im- 

 portant weeds to the biennial group. 

 Among them are the common thistle (bull thistle) and some 

 of its immediate relatives ; the burdock, skeleton weed, and 



Fig. 182. — 

 Squirrel-tail 

 grass. After 

 Weed. 



Fig. I S3 . — Lamb's 

 quarters. After Weed. 



