468 PRACTICAL BOTANY 



(4) Capacity for self-pollination (if necessary). 



(5) Good means of seed dispersal. 



(6) Capacity for rapid growth. 



(7) The ability to resist plant diseases. 



(8) Tolerance of shade (at least when young). 



(9) Tolerance of drought. 



(10) Tolerance of excessive water supply and lack of air 

 in the soil. 



(11) The ability to resist the effects of dust in choking 

 the stomata. 



(12) Capacity to thrive in poor soil. 



(13) Ability to retain vitality of seeds buried in the soil, 

 sometimes from fifteen to twenty-five years. 



(14) Unpalatableness, offensive smell, prickles, or other 

 disagreeable characteristics, which lessen the danger of being 

 eaten by animals. 



Few if any weeds have all the above-named characteristics 

 in a high degree, but many kinds of plants have the greater 

 part of them. Which characteristics are common to many 

 weeds of woodlands? of pastures? of lawns? of roadsides? 

 of cornfields? of fields of the small grains? Name some of 

 the weeds which you know that have the largest number of 

 the qualifications (1)-(14). Can you name any plant that 

 has both characteristics (9) and (10) ? 



433. Effectiveness of weed equipment. In most instances it 

 is easy to see how the characteristics listed in Sect. 432 enable 

 weeds to persist. Evidently a plant which, like the Russian 

 thistle, produces tens of thousands of seeds, or one which, 

 like the dandelion, scatters seeds for miles with the wind, is 

 likely to reproduce itself abundantly and to occupy any suit- 

 able bit of vacant ground. But there are other most effec- 

 tive qualifications which need a little explanation. If a sorrel 

 plant 1 (Fig. 353) is dug up carefully, it will usually be found 

 to have several others attached to it by the roots. This is 

 rapidly becoming one of the worst weeds in the United States, 

 1 Rumex Acetosella. 



