70 BULLETIN 7-91-, U. S. DEPARTMENT OF AGRICULTURE. 
entirely dependent upon seed. The seed crop is relatively high in 
viability. However, if the factor detrimental to progressive develop- 
ment of the vegetation is not corrected, these relatively short-lived 
perennials will sooner or later be superseded by plants of the first- 
weed stage. 
27. The profusion of weedy or nongrasslike plants and the lim- 
ited occurrence of grasses render the second-weed stage much better 
suited for sheep than for cattle and horses. 
28. The carrying capacity of the second-weed-stage type, acre 
for acre, is very much less, regardless of the class of stock grazed, 
than of the porcupine-grass-yellow-brush cover. In addition, a less 
solid fat is produced. 
29. Sheep make rapid gains on the second- weed-stage type early in 
the season when the herbage is succulent and tender. Cattle and 
horses, on the other hand, little more than maintain their weight 
even though the lands are lightly stocked. The vegetation matures 
early, after which the leafage is largely unpalatable to stock, and 
the herbage of many species is largely lost through the destructive 
effect of frost. Therefore the lands are of little value for grazing 
unless cropped early in the season. 
THE RTJDERAL-EARLY-WEED CONSOCIATION. 
30. On lands whose soils have been so seriously impaired that 
available water is similar in amount to that held by relatively newly 
formed soils recently invaded by herbaceous plants, the vegetation 
consists essentially of annual species characteristic of the first or 
early weed stage. 
31. The most typical and abundant species of the first-weed stage 
are goosefoot or lamb's-quarters, slender-leaved collomia, tarweed, 
Tolmie's orthocarpus, Douglas knotweed, and tansy mustard. Nu- 
merous less abundant species are associated with these. 
32. The seed habits of ruderal-weed plants are strong, the via- 
bility of the seed crop averaging considerably higher than that of 
the perennial species. 
33. Because of the entire dependence of the plants on seed for their 
regeneration and the fact that the conditions of the season are not 
always favorable to seed production or germination, there is wider 
variation in the density of the stand of the first-weed-stage cover 
from year to year than in that of any other consociation. 
34. Owing to the low fertility of the soil characteristic of the first- 
weed stage it contains less available moisture than soil of the higher 
ecological types. This tends to hold the development of the vege- 
tation in check. At the same time plants grown on inferior soils of 
this kind require appreciably more water for the production of a 
