1 8 WEEDS OF FARM LAND 



Ononis repens (restharrow). Broken pieces. 



Rhinanthus crista-galli (yellow rattle). Cut fragments and 



rooted plants. 



Rumex acetosella (sheep's sorrel). Cut fragments. 

 Stellaria media (chickweed). Rooted plants. 

 Vicia cracca (tufted vetch). Fragments. 



Further observation on this means of dispersal are very 

 desirable. Many weeds that are obviously distributed by means 

 of seeds have apparently no special adaptation for dispersal, 

 and yet there is no doubt that distribution does occur. It is 

 quite possible that all the agencies at work are not fully 

 known, and that wind carriage during gales and storm 

 columns is of far more importance than is at present believed. 



2. METHODS WHICH ARE DEPENDENT UPON SPECIAL 

 ADAPTATIONS FOR DISTRIBUTION DEVELOPED BY THE 

 PLANTS. 



Weeds having special adaptations that assist in their 

 distribution may be broadly divided into two classes according 

 as they are spread by means of 



A. fruits and seeds (sexual reproduction). 



B. vegetative parts (vegetative reproduction). 



The line of division is not always sharply marked, as in some 

 weeds both types of reproduction are well developed, but as a 

 general rule only one method is of real importance to a par- 

 ticular plant. Those in which both methods are conspicuous 

 comprise some of the worst of our agricultural weeds, as 

 methods of eradication that are directed against the formation 

 of seed are not always effective against the spread of vegeta- 

 tive parts and vice versa. This double-barrelled reproduction 

 is specially noteworthy in thistles, wild onion, corn sowthistle, 

 coltsfoot, and creeping buttercup, though it occurs to some 

 extent in various other weeds. In the following classification 

 the same weed may appear twice if the two methods of dis- 

 tribution are sufficiently well marked to warrant it. 



A. Distribution by Fruits and Seeds (Sexual Reproduction). 



(a) Seeds Produced in Large Quantities. Many weeds 

 that do not have special adaptations for seed distribution are 

 safeguarded by the production of large quantities of seeds, so 



