VQ BUULrETIIsr 791, U. S. DEPAETMENT OF AGRICULTURE. 



entirely dependent upon seed. The seed crop is relatively lligh 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 perennials will sooner or later be superseded by plants of the first- 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 tj^'pe, acre 

 for acre, is very much less, regardless of the class of stock grazed, 

 than of the porcupine-grass-yeilow-brush cover. In addition, a less 

 Bolid 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 

 earl}^, 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 RUDERAL-EARLT-WEED COXSOCIATION. 



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 coilomia, 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 



