MISTLETOE INJURY TO CONIFERS. 33 



P. ponderosa, but occurs on P. jeffreyi (5, p. 192), P. arizonica (2, 

 p. 243), and P. mayriana (2, p. 243). R. campylapoda has recently 

 been collected by the writer near Coeur d'Alene, Idaho, on P. contorta. 

 Sparingly distributed throughout the Northwest are some large forms 

 of Razoumofskya on Abies, Plants collected by the writer on Abies 

 grandis and A. concolor are apparently the same as that described by 

 Engelmann (3, v. 2, p. 106) on the former host under the name 

 Arceuthobium occidentals var. abietinum. Although it would prob- 

 ably be better on morphological grounds to refer this form to 

 R. campylopoda (Engelm.) Piper, as Engelmann's Arceuthobium 

 occidentale is now named, owing to its seeming close affinity to 

 the genus Abies and the absence of cross-inoculation data it could 

 well be raised to specific rank. These mistletoes in point of mor- 

 phology are in great contrast with the small forms on Abies previ- 

 ously mentioned. They may be considered typical of a group of 

 large forms occurring only on Abies. 



From the foregoing, it seems possible that the members of the genus 

 Razoumofskya may be arranged in a series of natural groups accord- 

 ing to their host relationships. It is also interesting to note that the 

 largest, the longest lived (both cortical and aerial parts), and the 

 most strictly parasitic forms are associated with the hard or yellow 

 pines. These pines exhibit anatomically a high differentiation. This 

 may throw some light on the nutrient relation of some mistletoes 

 to their hosts ; also their family peculiarities. 



SUGGESTIONS FOR CONTROL. 



It is clear from the foregoing pages that the damage to forest 

 growth by the mistletoes of coniferous trees in the Northwest is of 

 sufficient importance to receive the attention of every forester. Steps 

 should be taken in all logging operations, where local problems of 

 economy do not interfere, to make a beginning of the eradication of 

 mistletoe by marking every infected tree for cutting. In some cases it 

 would seem advisable to introduce into the contract a special clause 

 dealing wholly with mistletoe-infected trees. The most injurious of 

 the mistletoes of the genus Razoumofskya on coniferous trees, as indi- 

 cated, are in the main confined to their own particular hosts or to spe- 

 cial groups; hence, it is not advisable to establish in mistletoe regions 

 pure stands of a species much subject to attack. In this respect the 

 problem of the control of mistletoe is similar to that of forest-tree 

 fungi. Mistletoes being light-loving plants, close stands should be 

 maintained as much as possible on all exposed parts of the forest. 

 For the same reason rims of canyons and all exposed areas, such as 

 the borders of bench lands, natural parks, shores of lakes, etc.. should 

 be protected w T ith species which are not usually subject to the ravages 



