36 



BULLETIN" 791, U, S. DEPARTMENT OF AGEICTjLTURE. 



Table 2. — Average chemical properties of typical soil samples taken from the 

 surface to a depth of 6 inches of an area supporting a cover of foxglove, 

 sioeet sage, and yarrow, and of similar samples representing soil supporting 

 a cover of porcupine grass and yellow brush. 



Samples. 



Total 



lime 



(CaO). 



Carbon 

 dioxide 

 (COj). 



Calcium 

 carbo- 

 nates 



(CaCOs). 



Organic 

 carbon. 



Total 

 nitro- 

 gen. 



Nitrates 

 (parts 



per mil- 

 lion of 



dry soil). 



Total 

 organic 

 matter. 



Foxglove, sweet-sage, and yarrow 

 cover 



Percent. 

 1.03 



1.13 



Per cent. 

 0.08 



0.10 



Per cent. 

 0.18 



0.38 



Per cent. 

 1.52 



3.20 



Percent. 

 0.17 



0.35 



11 



17 



Per cent. 

 3.03 



Porcupine-grass and yellow-brusli 

 cover 



5.60 







The blue foxglove, sweet sage, and yarrow reproduce mainly by 

 means of rhizomes or rootstocks; and like most high mountain 

 plants which give rise to new individuals by vegetative means, their 

 seed habits are only moderately strong. Germination tests con- 

 ducted from 1914 to 1916, inclusive, gave the following average 

 percentages : 



Blue foxglove 11.8 



Sweet sage 14. 2 



Yarro\\'. 9.3 



In addition to the low viability of the well-filled seeds, a rather 

 small seed crop is produced, a large proportion of the flowers either 

 not being fertilized or failing to develop after fertilization. How- 

 ever, where the soil is exposed and conditions favor germination 

 and growth, seedlings of varying density and vigor are in evi- 

 dence. Three years are required for -the developmental cycle of most 

 species — that is, from the time of germination of the seed until the 

 resulting plant produces viable seed and gives rise to new individuals. 

 Some species send up one or more flower stalks late in the second 

 year following germination, but, as a rule, no fertile* seeds are pro- 

 duced until in the third year of growth. By the end of the third 

 season, the rootstocks are well formed, so that reproduction both 

 by vegetative means and by seed usually takes place more or less 

 simultaneously. 



THE EFFECT OF DISTURBING FACTORS. 



Like the vegetation composing the types already discussed, the 

 foxglove-sweet-sage-yarrow cover readily replaces itself where the 

 edaphic conditions are not appreciably changed as a result of the 

 cover being eliminated or thinned out. Where the physical or chemi- 

 cal conditions of the soil are rendered less favorable to growth than 

 formerly, however, several species lower in the succession promptly 

 gain dominion over the soil. Among the first and most reliable 



