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 fruits are furnished each with a balloon, or a sail, or with grappling hooks. (Dandelion, sticktights, burdock.) 12. Some remain with the dead plant long into winter, and when torn off by the wind or by birds, drift for long distances on the snow, often from one farm to another. (Pigweeds.) 13. Some have creeping root-stocks or tubers. (Quack-grass, nut-grass.) 14. Some defend themselves with forks and bayonets. (Thistles.) 15. Most of them are disagreeable in taste or odor, so that domestic animals leave them to occupy the ground and multiply. (Jamestown weed, stink grass, milk weed.) 16. Plants with stout roots are sometimes passed over by the harrow or cultivator. HOW ARE WEEDS INTRODUCED AND HOW ARE THEY SPREAD? 1. By live stock, carried in the hair or fleece or carried by the feet; in some instances passing alive with the excrement. 2. By unground feed-stuff purchased. 3. By adhering to the insides of sacks where they were placed with grain. 4. In barnyard manure drawn from town. 5. In the packing of trees, crockery, baled hay and straw. 6. By wagons, sleighs, threshing machines. 7. Sometimes by plows, cultivators and harrows. 8. By railway trains passing through or near a farm. 9. By ballast of boats at wharves. 10. By wool-waste at factories. 11. By birds, squirrels, and mice. 12. By water of brooks, rivers, by washing rains and by irrigating ditches. 13. By the wind aided by little wings or down, or by drifting on the snow. 14. By dropping seeds to the ground from extending branches and repeating the process. 15. By creeping root-stocks, as June grass, quack-grass and toad-flax.