CHAPTER II. 



DISTRIBUTION OF WEEDS. 



THE flora of any country or district usually comprises many 

 hundreds or thousands of species, but of these compara- 

 tively few are conspicuous as weeds of cultivation. This is to 

 a very great extent determined by the fact that cultural con- 

 ditions are mimical to the growth of many wild plants which 

 resent interference with their normal conditions of life. The 

 extent ofthe weed flora is further circumscribed by the fact that 

 many plants, though able to withstand the conditions peculiar 

 to cultivation, are so ill adapted to arrange for their own repro- 

 duction under the specialised circumstances that they fail to 

 maintain their position and are therefore practically unknown 

 as weeds. The most familiar and widespread weeds are those 

 plants which are the best adapted to meet the difficulties which 

 arise from the carrying on of the various operations of 

 cultivation. 



The methods ot weed distribution are many and various, 

 but may be broadly divided into two classes, though the divid- 

 ing line cannot always be sharply maintained : 



(1) Methods which are independent of any special adapta- 

 tions for distribution developed by the plants. 



(2) Methods which are dependent upon special adaptations 

 for distribution developed by the plants. 



i. METHODS WHICH ARE INDEPENDENT OF ANY SPECIAL 

 ADAPTATIONS FOR DISTRIBUTION DEVELOPED BY THE 

 PLANTS. 



(a) Various Means of Transport, as in Cargoes, Ballast, etc., 

 including the Transport of Impure Seed. Distribution by means 

 of transport must be held accountable for the spread into vari- 

 ous parts of the world of many of the worst weeds of culti- 

 vation. With the increase in trading facilities and the opening 

 up of fresh shipping routes there has come a notable change 



