Dwarf Mistletoes 



have also been reported from China 

 and constitute a problem in forest man- 

 agement in the Himalaya Mountains 

 of India. The dwarf species attack only 

 conifers and are not used for decora- 

 tive or symbolic purposes. 



Five species are recognized in North 

 America. One of them, A. pusillum, is 

 found only from the Great Lakes re- 

 gion east, mainly on spruce. The other 

 four, typically western, range from 

 Canada and Alaska to Mexico. Of 

 these four, one (A. americanum) is 

 confined to the ranges of lodgepole and 

 jack pine, another (A douglasii) to 

 the range of inland Douglas-fir. Of the 

 others, A. vaginatum is restricted to 

 three-needled pines, notably Pinus pon- 

 der osa var. scopulorum in the south- 

 western United States and Mexico, and 

 A. campylopodum attacks pine, spruce, 

 fir, hemlock, and larch from Alaska to 

 Arizona and, probably, Mexico. 



The dwarf mistletoes have been re- 

 ported in Arizona, California, Colo- 

 rado, Connecticut, Idaho, Maine, 

 Massachusetts, Michigan, Minnesota, 

 Montana, Nevada, New Hampshire, 

 New Jersey, New Mexico, New York, 

 Oregon, Pennsylvania, Rhode Island, 

 Texas (the northwestern part), Utah, 

 Vermont, Washington, Wisconsin, and 

 Wyoming. Although the list indicates 

 widespread occurrence from east to 

 west, it should be pointed out that none 

 has been found in the island of pon- 

 derosa pine covering the Black Hills of 

 South Dakota or in the great Douglas- 

 fir forests on the west side of the 

 Cascade Range north of the Umpqua- 

 Willamette Divide. It is also notable 

 that they do not attack the high-pro- 

 ducing forests of the South. In Texas 

 they are restricted to isolated mountain 

 ranges in the northwestern part of 

 the State, where the timber values are 

 negligible. 



THE DWARF MISTLETOES are leaf- 

 less, flowering plants. They are dioe- 

 cious that is, the staminate, or male, 

 flowers are borne on separate plants 

 from those producing the seed. The 

 root system of these parasites has 



459 



developed into an absorption system, 

 which can invade and maintain itself in 

 both the wood and the bark of its host. 



From the host it derives nutrients 

 and water. The absorption system has 

 been known to live for many years 

 within the tissues of the host plant 

 without producing aerial shoots. The 

 shoots are segmented stems, which may 

 or may not branch. In A. pusillum they 

 attain a height of about an inch and 

 are unbranched. In A. campylopodum 

 and A. vaginatum they may become 

 several inches long and are usually 

 branched. The primary (if not the 

 sole) function of the shoots is to pro- 

 duce flowers and fruits. Most of the 

 Phoradendrons, on the other hand, 

 appear capable of producing most of 

 their own food and are believed to rob 

 their host primarily of water and dis- 

 solved minerals. 



In all species except A. pusillum, the 

 fruits mature the second season after 

 pollination. They are berrylike struc- 

 tures that vary in color from light 

 green to blue green or even brown. In 

 size and shape they resemble a grain 

 of wheat. 



The outside casing, or skin, of the 

 fruit is a tough and elastic sac. At 

 maturity the sac contains the seed and 

 a hygroscopic material called viscin. 

 As the viscin absorbs water, pressure 

 against the elastic wall of the casing is 

 increased. When the seed is ripe the cas- 

 ing is ruptured from its base, leaving 

 one end of the sac open. Simultane- 

 ously, the wall of the casing contracts, 

 and the seed is forcibly ejected into 

 the air. The sterns, or pedicels, sup- 

 porting the ripe fruit curl downward 

 in such a way that the base of the 

 fruit points skyward at the time of 

 the explosion and the expelled seed 

 then follows a trajectory like a mortar 

 shell. Seed that are shot from 20 or 

 more feet above ground and allowed to 

 follow their course without obstruction 

 will usually travel from 20 to 40 feet 

 horizontally sometimes more than 60 

 feet. 



The seed carries with it a small 

 amount of the sticky viscin, which 



