WEEDS. 297 



Number of seeds on 

 a plant. 

 Foreign — Perennial — 



Canada thistle to 10,000 



Ox-eye daisy 800 to 95,000 



Sour dock 36,000 to 90,000 



Vitality, — Under the proper conditions seeds may 

 maintain their vitality for years. Jamestown weeds 

 have been known to grow in a piece of land for ten 

 years from a single seeding. A single plant contain- 

 ing 100,000 seeds may, therefore, be the source of 

 considerable annoyance, not to say expense. 



Beal buried twenty common varieties of weeds 

 seeds twenty inches deep in pint bottles of sand. 

 At the end of live years eight varieties failed to grow. 

 Of the twelve remaining varieties thirty-one oat of 

 fifty grew. Of purslane nineteen, of pig- weed 

 twenty -one, fox-tail thirty- four and of sour dock forty- 

 five out of fifty seeds grew at the end of five years. 



When, however, seeds are exposed to the usual con- 

 ditions of heat, moisture and aii-, many either grow or 

 rot. Our worst annuals are those which are prolific 

 and have the power of resisting these influences for a 

 long time. 



The reserve force of seeds is illustrated by the 

 cockle-burr. Each burr has two seeds. Ordinarily 

 only one of these grow. But if the plant is destroyed 

 the second seed grows. _ ._ ' 



Dissemin^nita.— ^lost of our worst weeds being 

 of foreign origm it follows that their presence de- 

 pends on some means of dissemination. These are 

 many and often curious and may be divided into two 

 general classes: natural and artificial. 



Distribution by wind is one of the most familiar 

 natural means. Many seeds of the sun -flower family, 



