6 BULLETIN 34, U. S. DEPARTMENT OF AGRICULTURE. 



smaller crop which matured at a later date; the weakest matured 

 practically no seed. 



An even closer correlation is found in the case of seed fertility. 

 The most vigorous plants matured their seed by August 20, with an 

 average germination power of 14 per cent; the less vigorous indi- 

 viduals matured their seed September 1, with an average fertility of 



7 per cent, while the very weakest produced mature seed September 

 12, the fertility of which averaged only 1.5 per cent. Weakened 

 vegetation, then, results in (1) late resumption of growth in the 

 spring and sparseness of herbage; (2) the production of few flower 

 stalks, the majority of these late in the season; (3) late maturity of 

 seed and a small seed crop which is either sterile or has a very low 

 fertility. 



SCATTERING AND PLANTING THE SEED. 



Almost immediately upon reaching maturity the seeds of the lead- 

 ing range plants are dropped. This is highly advantageous in that 

 it eliminates the possibility of stock consuming the crop after it has 

 been developed. The dissemination varies with the different species. 

 In the case of the grasses and grasslike plants, such as sedges and 

 rushes, the seed drops near the parent plant, while seeds from plants 

 like fireweecl and mountain dandelion, which have highly developed 

 contrivances for distribution by the wind, are carried great distances. 

 Plants of the latter kind do not usually occur in as dense stands as 

 grasses, but, on the other hand, are more widely distributed over the 

 range. 



The possibility of getting reproduction depends upon whether or 

 not the seed is able to force its way into the soil. The surface soil 

 dries out early in the season, and seeds which germinate on the sur- 

 face of the ground are unable to extend their limited root system 

 deep enough into the rich and moisture-laden soil. As a consequence 

 the plants soon die from drought. 



Under purely natural conditions the likelihood of the seeds getting 

 into the ground is governed largely by their size and structure. The 

 seeds of some of the most important plants, such as mountain bunch- 

 grass and mountain brome grass, for example, are large and chaffy, 

 and even though promptly dropped upon maturity in the autumn, 

 months before germination takes place, are usually found uncovered 

 on the surface of the ground in the spring. Round, heavy seeds, 

 like those of wild onion and some of the sedges, have little difficulty 

 in working beneath the surface soil. The seed of a few species, some 

 of little or no forage value, are provided with strong bristles, which 

 work them well into the ground. 



From what has just been said it is clear that if the seed is not 

 planted by artificial stirring of the soil the undesirable species may 

 become established at the expense of the valuable range plants. 



