578 WEEDS : GENERAL 



quickly, tend to smother all slow-growing crops. The ordinary 

 methods of multiplication of annuals is by means of seeds only, 

 and allowing them to run to seed on the land is the chief source 

 of their continuation. 



Biennial weeds take two growing seasons to complete their 

 life. The seed placed in the ground in spring germinates, and 

 during the first summer produces a plant with a fleshy tap root 

 and contracted stem. The leaves on the latter lie close to the 

 ground during the first season, and prepare a considerable 

 quantity of food which is stored up in the tap root. The plant 

 rests during the succeeding winter, and in the following spring 

 the terminal and latent buds of the short stem develop at the 

 expense of the stored food, and produce elongated shoots which 

 bear leaves and flowers. After ripening the seeds, the whole 

 plant dies away. 



Wild parsnip, carrot, burdock, some species of thistle, and 

 other plants are included in this class. 



A large number of weeds are perennial. Such plants last 

 many years, and during their lifetime may give rise to several 

 generations of plants. Like annuals and biennials they are cap- 

 able of multiplication by means of seeds, and very often possess 

 the power of vegetative reproduction as well. 



An example is seen in creeping buttercups, which, besides 

 producing seeds, sends out runners which grow along the surface 

 of the ground and take root at their tips. When rooted the 

 terminal bud of each runner becomes an independent plant, 

 capable of growth even when the connection with the parent is 

 severed. A repetition of the process follows in the newly- 

 established offspring and the plant thus rapidly spreads over 

 land without the special aid of seeds. A similar method of 

 vegetative reproduction is carried on in some instances by 

 means of stems which grow underneath the ground and 

 elongate and take root there. Perhaps the most familiar weeds 

 of this class are couch, wild mint, and lesser bindweed. On 



