155^ WEEDS AND PARASITIC FLOWERING PLANTS 



WEEDS AND PARASITIC FLOWERING PLANTS. 



1135- Razoumofskya spp. Mistletoes Injurious to Conifers in the United States — 



Weir, J. R., in United States Department of Agriculture, liulletii Xo. 360, pp. 1-39, Fig. 

 1-17, Washington, D. C, 1916. 



It is not generally known that the injury caused by several species 

 of Razoitmofskya [ArceutJiobium) to coniferous trees in certain localities of 

 the north western United States has attained to such proportions that the 

 question has assumed all the characters of a serious forest problem. The 

 species which suffer the most are : Western Larch {Larix occidentalis) ,VJes- 

 tern Yellow Pine {Pimis ponderosa), Lodgepole pine (P. contorta), and Dou- 

 glas Fir {Pseudotsuga taxifolia). F^ach of these hosts in attacked by a distinct 

 species of Razoumofskya : R. lands Piper ; R. campylopoda (Engelm.) Piper; 

 R. americana (Nutt.) Kuntze ; R. Douglasii (Engelm.) Kuntze. 



The most striking symptom of the disease is the gradual reduction of 

 the leaf surface, caused by the " witch's brooms " and by various outgrowths 

 which occur on the trunk and branches, and which in time can cause the 

 death of the host. In all the cases the development of the tree is seriously 

 retarded, as is shown in the following table : 



Host and condition 



Pinus contorta 



Infected . . . 



Uninfected . . 

 P. ponderosa 



Infected ... 



Uninfected . . 

 Larix occidentalis 



Infected ... 



Uninfected . . 

 Pseudotsuga taxifolia 



Infected ... 



Uninfected 



Average 



Age class 



Height 



Diameter 



breast high 



65 

 60 



100 ■ 

 100 



144 

 144 



97 

 97 



feet 



35-2 

 48.5 



49.5 

 77.2 



63.0 

 115.0 



62.0 

 73.0 



6.3 

 7-8 



l8.2 



22.2 



11.5 

 19.5 



173 



22.2 



Total 



annual 



growth 



in. 



0.93 

 2.93 



1-54 

 5.33 



1.28 

 2.154 



2.175 

 3.28 



One of the first effects of infection, either of branch or of trunk, is the 

 formation of a fusiform swelling, which is sometimes very pronounced and 

 resembles the enlargements caused by some species of Peridermium. On 

 the branches this swelUng is the first stage in the development of a 



