76 BULLETIlSr 365, U, S, DEPAETMEK"T OF AGEICULTURE. 



late in the season during the month of September the leaves of Del- 

 fhinium harheyi 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 harheyi will be 

 stripped from the stems by the grazing cattle and eaten with no re- 

 sulting harm. 



The chart for DelphiniuTn 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 DelphiniuiTb tnemiesii 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, Delphiniurrh Tnensiesiiis 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 DelpJiinium msmiesii 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 harheyi 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 

 Delphiniwm cucullatum varies in its toxicity as does Delphinium 

 harbeyi. 



Investigations in the Sierras, where the common larkspur is Del- 

 phiniumj 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. 



