374 YOUNGKEN— ON THE MYRICACEAE 



In due course of time, as is evidenced in many older infested cells, the 

 fungal threads become shrunken together and impregnated with gummy 

 lignin forming a good sized lump of degenerating material within the 

 cell, which remains connected with similar lumps, or mycelial webs of 

 adjacent cells by means of threads which penetrate the cell wall. Some 

 of the cells containing the rosettes also show coccus-Uke forms, while 

 other cells, especially in the older basal portion of the tubercle, are almost 

 completely filled with these. These cocci are probably products of the 

 disintegration of the filament. They may be involution forms of the 

 Actinomyces organism which appear in cells whose contents are poorly 

 adapted to the trophic needs of the endophyte. Their presence in such 

 numbers on artificial culture media would support this hypothesis. 

 While Actinomyces is the primary infecting agent responsible for the 

 tubercles on Comptonia asplenifolia, there frequently later appears in 

 the cells and intercellular air-spaces of some of the tubercles a mycelium 

 producing fungus with unseptate hyphae belonging probably to the 

 Oomycetes as Harshberger suggested. The h>T3hae of this fungus are 

 several times as thick as those of Actinomyces. They penetrate through 

 the cell walls of the tubercle, passing from cell to cell and often coil up 

 into a mycelial mass in many of the cells invaded (Plate 88, Fig. 27). 



Since Actinomyces is frequently a virulent pathogenic organism in 

 cattle and other domestic animals up to man, because the swellings it 

 produces on plants are analagous to those on animals, since the forms of 

 the organism as shown by Jordan^** in the infested lesions of animals are 

 similar to those which the writer has described in the lesions of Myrica, 

 and since the cultural characteristics of the organism isolated from the 

 lesions of animals by Wright,^' Wolff and IsraeP^ are in many respects 

 similar to those isolated from the Myricas and described by the writer, 

 he would regard the organism as a parasite and suggest its possible 

 pathogenic relation to such animals. 



The Actinomyces not only confines itself to the cortex of the tubercular 

 roots, it later works its way into the tracheae of these structures, passes 

 into the pitted vessels of the main roots, thence into those of the stems, 

 and, conveyed by the transpiration stream gradually upward is carried 

 through the axes of catkins so as finally to reach the flowers, bracts and 

 fruits. In these it confines its existence to the parts corresponding to the 

 mediocortex of the root tubercles, namely the mesophyll and outer 

 mesocarp regions respectively. 



The writer having isolated the organism in pure culture from the 

 lesion produced by it on the seedUng tubercles hereby assigns to it the 

 name Actinomyces myricarum. 



