336 



INTRODUCTION TO BOTANY 



6. Poisonous or intoxicating plants injure horses, cattle, and 

 sheep. 



7. Some spiny plants (such as the smaller cacti) and burs 

 (like the sand bur) may lame the feet of domestic animals. 



Thorny shrubs are very 

 troublesome to woolgrow- 

 ers, as they pull out much 

 wool, and the burs greatly 

 injure the quality of the 

 fleece. 



8. Certain weeds, when 

 eaten by cows, render milk 

 unpalatable or ill-scented. 



9. Weed seeds injure the 

 quality and affect the price 

 of clover and other seeds 

 that are raised for sale. 



313. Amount of damage 

 caused by weeds. It is im- 

 possible to put into exact 

 figures the amount of dam- 

 age annually done by weeds 

 in the United States, but 

 it probably aggregates over 

 1200,000,000 a year. 1 



The expense caused by 

 weeds is largely for extra 

 labor of men and animals, 



FIG. 243. Clover dodder, parasitic on 

 red clover 



A, habit sketch of part of the parasite and 

 the host ; B, portion of stem of the dodder, 

 showing protuberances from which haus- 

 toria pass into the stem of the host ; (7, 

 a single flower of the dodder. B and 

 considerably magnified. Modified after 

 " Flora Danica " 



1 The estimate here given is by 

 Professor Frederick V. Coville, 

 and is based on the assumption 

 that the loss may amount to 5 

 per cent of the total value of the 



principal crops of the United States. The estimated value of the crop of 

 corn, wheat, oats, barley, rye, buckwheat, flaxseed, rice, potatoes, hay, 

 tobacco, and cotton for the year 1912 was $4,693,000,000. 



Another estimate by an expert in the Department of Agriculture places 

 the loss at about $300,000,000. 



