INTRODUCTORY 11 



Annuals complete their growth in a year. As a rule, they 

 have small fibrous roots and produce a large quantity of seed. 

 Examples of this class are Wild Mustard, Lamb's Quarters, 

 Wild Buckwheat, Purslane, Ragweed and Wild Oats. Some weeds, 

 called Winter Annuals, are true annuals when the seeds ger- 

 minate in the spring, but they are also biennial in habit; that is, 

 their seeds ripen in the summer, fall to the ground, germinate 

 and produce a certain growth before winter sets in, and then 

 complete their development the next spring. Of these may be 

 mentioned Shepherd's Purse, Peppergrass, Stinkweed, Worm- 

 seed Mustard, Ball Mustard, Hare's-ear Mustard, Canada Flea- 

 bane anjd Blue Bur. 



Biennials require two seasons to complete their growth, 

 the first being spent in collecting and storing up a supply of 

 nourishment, which is used the second season in producing 

 flowers and seeds. Examples of these are Burdock, False 

 Tansy, Common Evening Primrose and Viper's Bugloss or Blue- 

 weed. 



Perennials are those plants which continue to grow for 

 many years. Perennial weeds are propagated in several ways, 

 but all produce seeds as well. They have two distinct modes 

 of growth; some root deeply, while with others the root system 

 is near the surface. The most troublesome are those which 

 extend long underground stems or rootstocks beneath the 

 surface of the ground, as Canada Thistle, Perennial or Field 

 Sow Thistle, Field Bindweed, Bladder Campion, White-stemmed 

 Evening Primrose, Blue Lettuce and some wild sunflowers. 

 Representatives of the second class or shallow-rooted perennials 

 are Pasture Sage, Yarrow and Couch Grass. Some perennials 

 extend but slowly from the root by short stems or offsets, but 

 produce a large quantity of seed. Of these, Ox-eye Daisy, 

 Dandelion, Goldenrod and Yarrow are examples. 



Weeds might also be grouped, according to their manner 

 of distribution, into two general classes : 



a. Weeds distributed in time are those which, when mature, 

 discharge their seed close to the mother plant. The seeds of 



