488 PROCEEDINGS OF THE ACADEMY OF [^^^Y, 



The hyplia, as it passes through the area of the bordered pit, en- 

 larges to fill the space formed when the middle lamella of the cell 

 Avail at this point is dissolved by ferment action (fig. 24a). The 

 hypha at this point, therefore, becomes in shape like a double 

 convex lens. Again, a hypha that runs in general longitudi- 

 nally in the tracheids may leave these and enter a medullary 

 ray cell, where it courses transversely, enlarging meanwhile in 

 the medullary ray cell and giving off short rounded branches 

 which may be called tentatively haustoria. A hypha that enters 

 a tracheid in one direction may form two branches, one a short, 

 lateral, downward -directed branch that ends in one of the large 

 ventricose cells (fig. 27) to which reference has been made, and 

 another branch which runs to the end of the tracheid and leaves it 

 through a bordered pit to enler another tracheid. xinother hypha 

 runs lengthwise until it comes opposite lo the pointed end of an- 

 other tracheid, where a row of five bordered pits is seen in trans- 

 verse section. For each of these bordered pits the longitudinal 

 hypha gives off a branch (figs. 24, 24a). Each branch thus 

 formed swells in the space of the bordered pit to form a lens like 

 enlargement before the branch enters the contracted lumen at the 

 pointed end of the other tracheid. All of these appearances are 

 illustrated in the annexed figures (figs. 24, 24a, 25, 26, 27, 28). 



The course of the hyphse in the areas of stem that have been trans- 

 formed pathologically into a broken-down mass of a brown color, 

 forming pockets throughout the Avood, is more irregular. Here 

 the hyphfe forming the mycelium bend and twist about, now form- 

 ing an enlarged ventricose hyphal cell, and again producing such a 

 swollen cell as the termination of a short lateral branch. Short 

 stubby branches are also formed in the course of these same 

 hyphie, consisting in most cases of a single short cell. The hyphse 

 of these brown areas have also increased considerably in diameter, 

 being much thicker than those of the mycelium Avhich grows in 

 the tracheids. The larger hyphse are found in the cleft-like inter- 

 cellular spaces and grow in and out between the dead and broken- 

 down cells, as well as through the resin-like substance which fills 

 the pockets to which reference has been made above. 



The hyphse in the smaller transverse sections of the diseased stem 

 are also clearly traceable. They are seen as purplish-brown rings 

 in the lumen of the tracheids (figs. 20, 21). Several adjacent 



