76 BULLETIN" 365, U. S. DEPARTMENT OF AGRICULTURE. 
late in the season during the month of September the leaves of Del- 
phinium barbeyi are eaten by stock with great apparent eagerness. 
Before the season is concluded, where a range is grazed with any 
thoroughness, nearly all the leaves of Delphinium barbeyi will be 
stripped from the stems by the grazing cattle and eaten with no re- 
sulting harm. 
The chart for Delphinium menziesii, figure 9, determined by the 
experiments of 1910. would seem to indicate that the quantity neces- 
sary to poison stock grows smaller as the season progresses. This 
probably is explained by the fact that in the latter part of June 
many of the plants have formed seed and that these seed pods were 
eaten by the cattle. If the plant has greater toxicity in the latter 
part of the season than in the earlier, as this chart would seem to in- 
dicate, it is doubtless explained in this way, for the seeds are formed 
in Delphinium menziesii while the leaves are still more or less green 
and doubtless attractive to a grazing animal. 
The principal inferences from these facts in regard to the variation 
of toxicity with the age of the plant may be summed up as follows : 
First, Delphinium menziesii is poisonous during the whole period 
of the life of the plant. Immediately upon the formation of the 
seed, the plant withers and disappears, so that it no longer is a 
factor in poisoning. If Delphinium menziesii does more harm in 
the early season than in the latter period of its existence, it must be 
due to the fact that, because of the poorer feed earlier in the season, 
cattle may eat more of it than they do later when the grasses have 
sprung up. 
Second, Delphinium barbeyi in Colorado is poisonous from early 
spring until the middle or last of August, its toxicity after blossom- 
ing gradually diminishing until it entirely disappears and the plant 
can be eaten with impunity by cattle. It would appear that it is 
vastly more toxic early in the season and without doubt it is in the 
month of June that the most harm is done by this plant. The fact 
of the great toxicity of the seeds has little practical importance be- 
cause cattle rarely feed upon them. So far as inferences may be 
drawn from a somewhat limited experience it would appear that 
Delphinium cucullatum varies in its toxicity as does Delphinium 
barbeyi. 
Investigations in the Sierras, where the common larkspur is Del- 
phinium glaucum, show a somewhat different condition from that 
noted in Colorado. Here the snowfall is very heavy and the snow 
does not disappear in some localities until very late in the season, 
making the period of blossoming late. Larkspurs may be in blossom 
as late as September, and the period of possible poisoning of cattle 
is extended through nearly the whole grazing season. 
