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. 
Fic. 248. 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; C, 
a single flower of the dodder. B and ( 
considerably magnified. Modified after 
“Flora Danica” 
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 
$200,000,000 a year.1 
The expense caused by 
weeds is largely for extra 
labor of men and animals, 
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. 
