570 Forestry Quarterly 



inconspicuous and their presence is chiefly recognized by the 

 accompanying hypertrophy of trunk or branch. These mistletoes 

 are propagated by means of seeds which are expelled with suffi- 

 cient force from the seed capsule to carry them several feet. The 

 thin layer of mucilage on the seed causes it to adhere to what- 

 ever it strikes. When a lodgment is found on tender imsuber- 

 ized parts of seedlings or of more mattire growth, the young ger- 

 minating plant penetrates the cortex and bast, and infection re- 

 sults. An elaborate perennial cortical root system results from 

 this infection and from it springs the leafless mistletoe plant. All 

 species of the genus are normally dioecious but staminate and 

 pistillate plants may occur in juxtaposition on the same twig, in 

 fact they often appear to spring from the same cortical stroma. 

 The first primary root (sinker) will penetrate as far into the cam- 

 biimi and cells of the newly formed wood as the tenderness of 

 these tissues will allow, this depending upon the age of the branch 

 infected. The depth to which this primary sinker penetrates at its 

 first elongation is as far as it ever goes. On the other hand, there 

 is in that part of the sinker coinciding with the cambium of the 

 host a zone of meristematic tissue which enables the sinker to 

 elongate at this point, keeping pace with the increasing diameter of 

 the branch. After a time the lateral roots are developed from the 

 primary sinker and may extend for several feet in either direction 

 from the point of original infection. In some species this lateral 

 root system elongates with the branch, keeping pace with the last 

 third or fourth internode. Additional sinkers penetrate the deeper 

 tissues of the bast, springing from the transverse and longitudinal 

 root system, so that eventually a thorough infection of the entire 

 circimiference of the branch results. In very young stems the 

 primary sinker follows those sets of cells offering the least resis- 

 tance. Hence a cross section usually shows the medullary rays 

 occupied by these haustoria. 



The degree of parasitism attained by these parasites is far 

 greater than that of the Phoradendrons, or the true mistletoes, 

 which with one or two exceptions have large leafy branches and 

 rarely occur on conifers in America. The total reduction of the 

 leaves to mere bracts, together with a greatly reduced chlorophyll 

 content of the stems, is a first evidence of the class relation of the 

 false mistletoes with their hosts. A recent study made by the 

 writer of the more minute details of the anatomy of the sinkers and 



