358 PROCEEDINGS OF THE ACADEMY OF [May, 



goiis material. In the older normal roots, the cortex is dehmited by 

 a discontinuous layer of hard bast patches, a few elements of which are 

 occasionally met with in the galls. External to the rather abundant 

 brown cortex region of normal and fungous inhabited roots is a phello- 

 genetic layer, succeeded at the periphery by the young and old cork 

 cells. Where branches arise, a section at such places shows the 

 obhquely cut xylem pushing out surrounded by the cortex cells. The 

 young hght-colored cork cells at such places become confluent \vdth 

 the similarly colored wood cells, so that it is difficult to distinguish 

 between the elements composing these two distinct kinds of tissue. 

 Another marked feature in both the normal and parasitized roots is the 

 plugged tracheids with a yellowish or brown gummy material,^* 

 whether in the nature of modified tyloses the writer was unable to 

 determine. The most highly modified portions of the roots of Myrica 

 cerifera, when parasitized by Frankia brunchorstii, are the woody 

 cylinder, the soft bast and the cortex. 



The finest fungous mycelium is found in the cortex of the younger 

 roots and growing into the medullary ray cells. It consists of fine 

 unicellular hyphse and can be made out with the greatest difficulty by 

 a No. 3 Leitz objective. With a No. 7 Leitz objective, the finer 

 hyphae become defined as cobweb-like threads stretching across the 

 large, lacunar, intercellular spaces which have been formed between the 

 rounded cortex cells near the apical portion of the swelling (PL XVII, 

 fig. 66). Sometimes the hyphae stretch straight across these inter- 

 cellular spaces, but more often they take a sinuous course and form a 

 complex where several branches cross each other (PI. XVII, fig. 3). 

 These finer hyphse are formed as branches from thicker brown hyphse 

 to be described later. 



The course of the hyphse, as revealed in a longitudinal section of the 

 apical portion of the mycodomatial branches, is in general from cell to 

 cell. The hyphse may pass from one side of the cell to the other, pass- 

 ing out again through the cell wall, or the hyphse may make a loop, a 

 half turn or branch by the formation of short branches (PI. XVII, 

 fig. 6). These short branches are found imbedded in the protoplasm 

 of the cortex cells and may be looked upon in some sense as haustoria. 

 Sometimes several hyphse run into one host cell, and in such cases the 

 branches form a mesh. The hyphse also grow intercellularly. In 

 several transverse sections studied, three hyphae parallel to each other 

 pierce the same cell wall and run through the protoplasm of the cell 



^^ Harshberger, "Two Fungous Diseases of the White Cedar," Proc. Acad. 

 Nat. Sci. of Phiki., 1902. p. 461. 



