86 WEEDS OF FARM LAND 



they have any opportunity of flowering and seeding. As they 

 have no other means of propagation it is obvious that biennials 

 have a very poor chance under these circumstances except in 

 the isolated cases in which for any reason a change to an 

 annual habit is made. Consequently few or no biennials are 

 to be found among arable weeds, and even those of grass-land 

 are few in number, the most noteworthy being wild carrot, 

 spear thistle and marsh thistle, the hemlock from the border 

 of the fields being similar in type. 



(3) Perennial Weeds. These are plants which have no 

 definite term of existence, but which, when once established, 

 and if left to their own devices, live on from year to year, 

 constantly spreading and increasing in quantity. All of them 

 can and do arise from seeds, but they are by no means depen- 

 dent on this method for their perpetuation. Perennials have 

 various arrangements for vegetative reproduction whereby new 

 plants can arise from different portions of the original parent 

 without the intervention of seed. They also form thickened 

 and creeping underground stems, bulbs, or strong bulky roots, in 

 which quantities of food are stored up for the use of the plant 

 when necessary. Most of the perennial farm weeds die down 

 to the surface of the ground in the winter but live on in their 

 buried parts, and then, in the spring, the stored up food is 

 utilised to give the plant a fresh start and to carry it on until 

 the new aerial stem and leaves are able to take up the work 

 of nutrition. Fuller details of the habit of the perennials will 

 be found under the next heading " Habits of Growth of Weeds," 

 especially in sections 3, 5, 6, 8, 9. 



Habits of Growth of Weeds. Farm weeds vary much in 

 their habits, so that for every condition of life weeds are 

 found to suit the particular circumstances. Broadly speak- 

 ing, annual plants adopt one set of habits and perennials 

 another, but this is not an absolutely hard and fast rule. It 

 is not always possible to be quite certain how to classify some 

 weeds, as their mode of growth may combine the characteristics 

 of two classes, and the following grouping must only be 

 regarded as a broad and general division, which is liable to be 

 modified by different observers or by the same observer at 

 different times and places. 



(i) Erect Weeds. Under this heading may be classed all 

 those weeds which throw up an erect stem, more or less 

 branched, bearing leaves, flowers and fruit. Nearly all weeds 



