36 
BULLETIN 791, TJ. S. DEPARTMENT OF AGRICULTURE. 
Table 2. — Average chemical properties of typical soil samples taken from the 
surface to a depth of 6 inches of an area supporting a rover of foxglove, 
sweet sage, and yarrow, and of similar samples representing soil supporting 
a cover of porcupine grass and yelloiv brush. 
Samples. 
Total Carbon 
lime dioxide 
(CaO). (C0 2 ). 
Calcium 
carbo- 
nates 
(CaC0 3 ). 
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 
Percent. 
0.18 
0.38 
Percent. 
1.52 
3.20 
Percent. 
0.17 
0.35 
11 
17 
Per cent. 
3.03 
Porcupine-grass and yellow-brush 
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 
Yarrow. 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 
