10. A few make "Hair balls" in the stomachs of horses. (Rabbit-foot
clover, crimson clover.)

11. Some injure the quality of dairy products. (Leeks, wild onions.)

12. Penny cress, and probably others, when eaten by animals, injure the
taste of meat.

13. Poison hemlock, spotted cowbane and Jamestown weed are very
poisonous.

14. Many weeds interfere with a rotation of crops.

15. All weeds damage the appearance of a farm and render it less
valuable. (Quack-grass, Canada thistle, plantains.)

SOME SMALL BENEFITS.

1. They are of some use in the world to induce more frequent and more
thorough cultivation, which benefits crops.

2. The new arrival of a weed of first rank stimulates watchfulness.
(Russian thistle.)

3. In occupying the soil after a crop has been removed they prevent the
loss of fertility by shading the ground.

4. Weeds plowed under add some humus and fertility to the soil, though
in a very much less degree than clover or cow peas.

5. Some of them furnish food for birds in winter.

WHAT ENABLES A PLANT TO BECOME A WEED.

1. Sometimes by producing an enormous number of weeds. (A large plant of
purslane, 1,250,000 seeds; a patch of daisy fleabane, 3,000 to a square
inch.)

2. In other cases by the great vitality of their seeds. Shepherd's
purse, mustard, purslane, pigeon-grass, pigweeds, pepper-grass, May
weed, evening primrose, smart weed, narrow-leaved dock, two chick-weeds
survive when buried in the soil thirty years at least, as I have found
by actual test.

3. In each prickly fruit of a cocklebur there are two seeds, only one of
which grows the first year, the other surviving to grow the second year.

4. Some are very succulent, and ripen seeds even when pulled.
(Purslane.)

5. Often by ripening and scattering seeds before the cultivated crop is
mature. (Red root, fleabane.)

6. Sometimes by ripening seeds at the time of harvesting a crop, when
all are harvested together. (Chess, cockle.)

7. Some seeds are difficult to separate from seeds of the crop
cultivated. (Sorrel, mustard, narrow-leaved plantain in seeds of red
clover and alfalfa.)

8. Some are very small and escape notice. (Mullein, fleabane.)

9. Some plants go to seed long before suspected, as no showy flowers
announce the time of bloom. (Pigweeds.)

10. In a few cases the plants break loose from the soil when mature and
become tumble-weeds. (Some pigweeds, Russian thistle.)

11. Some seeds and seed-like f