114 
IOWA ACADEMY SCIENCES 
Pinus scojrdl:.. am : in the octhlils of the front range west of Fort Collins 
in one case, fl.t.v per cent, of the trees were affected and many had been 
killed, kike Arceiithobium americanum it produces large fascicled 
branches, as many as a half dozen may occur upon a single tree and ulti- 
mately destroy it. 
The last species here considered. A. douglasli Engelm. was found once 
in the Uintah Mountains on the south side of the range; the writer has 
also observed it in Clear Creek canon on Pscudotsuga douglasii. 
It produces small slender branches, one-fourth to one inch high, 
nearly erect, with flowers in short usually 5-flowered spikes; staminate 
flowers small or narrow with orbicular acutish lobes fruit two and one- 
half lines long. Dr. Bngelmann^ in speaking of the character of this 
species says, “Similar to the last, but smaller and never with verticillate 
branchlets or flowers, which are so common in that species. The thallus- 
liKe tissue or stroma, which creeps along v\^ithin the bark of the host 
plant, buds out in autumn all along the three years old shoot; after about 
twelve months, the flower-buds are formed, to open in the following- 
spring, after which the life of the male plant is exhausted; but it takes 
another year to perfect the fruit. The female parasite, now fully three 
years old, generally dies, but sometimes leaves and fructifles another sea- 
son. The Northeastern A. pusiJlum, Peck, behaves in the same manner, 
while in A. americanum and some other species the buds of the parasite 
make their appearance at first only among the older bud-scales of the 
pine branch.” 
Economic Considerations. The presence of these parasites upon their 
respective hosts is injurious to the timber, causing the same to become 
brown and brittle and wholly unfit for lumbering purposes. The growths 
may be held in check by cutting off diseased young branches, as they are 
the first attacked and may be considered centers of infection. The writer 
has seldom seen these parasites destructive in dense timber. 
Dr. Hermann Von Schrenk has long been interested in these parasites. 
It is to be hoped that a thorough study may be made of their specific 
characters as well as of their injurious effects since they include some of 
the most destructive of all of the parasitic diseases of the different coni- 
fers of the Rocky Mountain region. 
1. The siiecies \vas described by Engelraann in AVlieeler U. S. Geographical 
Survey west of the 100th meridian G : 25o. 
