THE WESTERTiJ" YELLOW PUsTE MISTLETOE. 29 



of the parent tree which may be transmitted through the seed, such 

 as an imusual divergence from the typical silvical characteristics of 

 the species. A clearer conception of the latent possibilities of dis- 

 ease resistance and immunity of a species obtained through tree 

 breeding is of vast importance in the sUvicultural improvement and 

 management of the forest. The hereditary influence of the parents 

 upon the offspring is a weU-recognized factor in genetics. This factor 

 is doubly important in forestry, not only in the collection of seed for 

 artificial regeneration, but also in the selection of seed trees to provide 

 for the natural reproduction of cut-over forests. In timber-sale prac- 

 tice only thrifty seed trees should be left and all diseased and sup- 

 pressed trees should be removed in order to improve the condition of 

 the forests of the future. 



SILVICULTURAL ASPECT OF MISTLETOE INFECTION. 



The destruction caused by disease promises to approach or even 

 surpass the losses from fire on the national forests of the Southwest, 

 now that the development of fire protection has reduced the fire 

 hazard. ^listletoe injury presents one of the most serious phases of 

 this silvicultural problem. The parasite may be slow in effecting its 

 injury, but it is unquestionably sure. 



A brief discussion of some of the salient objects of silviculture is 

 essential to a complete understanding of the significance of any 

 methods of control which may be attempted. The chief fundamen- 

 tals of silviculture, as applied in the regeneration of western yellow 

 pine stands, are to maintain the continuity of the forest and to 

 increase its productivity. A number of basic considerations must 

 be taken into account under any rational method of cutting, among 

 which may be mentioned the silvics of the species, the fire hazard 

 and liability, exploitation and economic conditions, and the removal 

 of the decadent, unhealthy, and overmature timber as rapidly as 

 possible, to avoid waste through decay. All defective, diseased, and 

 suppressed trees should be marked for cutting unless needed as fire 

 insurance or seed trees. No defective or diseased tree should be left 

 standing if it is evident that it will not live until the next cutting, 

 unless it is absolutely required for silvicultural purposes. When it 

 becomes necessary to reserve trees among the large dia.meter classes, 

 thrifty, healthy trees of good form should be selected, since the con- 

 dition of the progeny is influenced by heredity as well as by soil and 

 climate. Increased forest productivity will be realized if, in the 

 application of the above principles, the forester will also strive to 

 eliminate the deterioration of merchantable material. It is thus 

 evident that the marking on each individual area must be varied to 

 meet the sUvicultural requirements of the forest. The importance 

 of careful, intelligent marking on timber-sale areas can not be over- 



