Mistletoe Control 571 



horizontal root system of the parasite in relation to the tissues of 

 the host shows quite positively a close union between the two. 

 The phloem of the host is fotmd to be in some species in direct 

 imion with the absorbing cells of the parasite. The gradual weak- 

 ening of yoting trees imder the drain of a heavy infection of mis- 

 tletoe can hardly be brought about unless a certain part of the 

 organic food materials prepared by the host were not utilized by 

 the parasite. In older growth, suppression may be brought about 

 by the lopping of branches due to the formation of heavy brooms 

 on them and the destruction of the living circvimference by the 

 formation of burls on the main trunk. The fact that a great mass 

 of cortical roots often girdling the entire circumference of large 

 forest trees may remain living indefinitely without aerial parts is 

 additional evidence of the parasitic nature of these mistletoes. 

 Usually the different species of the genus Razoumofskya are con- 

 fined to particular forest trees or to those closely related. Unless 

 the mistletoe seed falls on a host on which it can live, the seed will 

 exhaust its energy in producing a long hypocotyl, but can not pene- 

 trate the substratimi. This indicates a special adaptation to the 

 particular types of cell structm"e or chemical constitution of the 

 different hosts. This in itself is significant in the light of the fore- 

 going statements. These are also important points to remember 

 in planning the management of some mixed forests. 



Our knowledge of the injurious effects of mistletoes is quite 

 sufficient to show the need of adopting some policy of forest man- 

 agement aimed at reducing the damage caused by those parasites 

 and attendant diseases. It will first be found necessary before 

 any organized attempt is made in this direction to arrange for 

 very effective stirvey work. The first step then would be to 

 conduct careful surveys of all forests wherever mistletoes are a 

 serious factor in the deterioration of timber. Since it will be 

 found that these parasites follow very distinct predilections as to 

 type of stand, topography, and to a certain extent, climate, the 

 zones of greatest mistletoe infection may be quite readily deter- 

 mined. It will hardly be possible for one or two men to do 

 effective work of this kind by merely going over the forest. The 

 survey should consist of a detailed statement of types, age classes 

 affected, and relation to topography. More effective results 

 could be obtained by carrying the record of mistletoe infec- 

 tion along with the regular yearly reconnaissance as it now being 



