372 Journal of Agricultural Research voi. iv, N04. 



R. americana contained mature spores; hence, the life cycle of the fungus 

 in the seed capsule is complete in the fall of the second year coincident 

 with the time required for the ripening of the seeds of the host. 



Soon after the conclusion of the experiments, a swamp area in the 

 Kaniksu National Forest, Idaho, scatteringly timbered by lodgepole 

 pine, was visited. The trees were heavily infected with the mistletoes 

 characteristic of this tree. A close examination of the mistletoe plants 

 showed them to be uniformly attacked by the fungus throughout the 

 entire area. So abundant was the fungus that very few of the pistillate 

 plants on any of the trees had escaped attack. This area has been a 

 fruitful source of investigation and a number of important facts have been 

 gathered. 



SIGNIFICANCE OF THE FUNGUS TO THE TAXONOMY OF ITS HOSTS 



The hosts of W. arceuthobii, so far as known at present, are as follows: 

 Razoumofskya pjisilla (Peck) Kuntze on Picea mariana. 

 R. americana (Nutt.) Kuntze on Pinus contorta. 

 R. douglasii (Engelm.) Kuntze on Pseudotsuga taxifolia. 

 R. douglasii, var. abietina Engelm., on Abies grandis and A. lasiocarpa. 

 R. douglasii, var. microcarpa Engelm., on Picea engeltnanni. 



A glance at the foregoing list shows a very interesting association of 

 mistletoes. The form on A. lasiocarpa (PI. LV, fig. 3), as known to the 

 writer, in point of morphology, color, and the time of maturity of pollen 

 and seed, coincides with the form on A. grandis (PI. LV, fig. 2). The 

 mistletoe on Picea engeltnanni is slightly smaller, often very much so 

 (PI. LV, fig. 4), but its other characteristics are the same. Comparing 

 these mistletoes with R. douglasii and R. pusilla, there is at once a marked 

 similarity among all five. They do not vary widely in form and color 

 of the stems. There is some variation in point of distribution of the 

 individual plants on the branch, whether aggregated or appearing singly. 

 Any one mistletoe, however, may exhibit both or either condition. The 

 staminate flowers of all five are a deep rich purple. No other species of 

 the genus possesses this character to such a marked degree. All five 

 bloom at the same time in the same latitude and exposure, and the seeds 

 ripen and are expelled in the same month. 



The question naturally arises, What is the true taxonomic position 

 of these mistletoes? Engelmann recognized the close affinities of the 

 small forms on spruce and fir to R. douglasii and named them varie- 

 ties of that species. The isolated and infrequent occurrence of these 

 small mistletoes on spruce and fir in the West should throw some light 

 on their probable relationships. If they are specifically distinct, they 

 should show greater activity in attacking their hosts. As it is, a single 

 tree will bear a few plants (broom formation) and the most diligent search 

 on the same host for miles around will not reveal a second infection. 

 The discovery of W. arceuthobii on those forms or species of the same 



