1902.] NATURAL SCIEXCES OF PHILADELPHIA. 485 



hyphfe arc uowhere abundant, and where tliey do occur they seem 

 to grow with the tracheids. The evidence of intracellular growth is 

 clear. =■' In one set of medullary ray cells a hypha is found which 

 forms an enlargement against a transverse partition wall before 

 penetrating it by secretion of a ferment (fig. 22). Fortunately 

 for clearness of observation, the end walls of two adjoining cells 

 are slightly separated, leaving a lens-like intercellular space (fig. 

 23). Through this space the hypha, contracted to a narrow thread- 

 like bridge, is seen to pass, enlarging again on the other side (fig. 

 23). The hypha which thus penetrates the cell wall passes to 

 the other end of the same medullary cell, where it enlarges into a 

 knob like extremity (fig. 23). It, however, gives rise to a branch 

 in the middle of the medullary ray cell. This branch grows out 

 transvei-sely by means of a bordered pit into the lumen of a wood 

 tracheid, through which it runs to the next medullary ray lying 

 parallel to the first. Here a new branch is found at right angles 

 to its former course through the tracheid, which enters a medullary 

 ray cell. This branch in turn produces another one at right angles 

 to itself, and this again another one which runs into new medullary 

 ray cells. The description of the course of this hypha, which is 

 clearly traceable in the longitudinal section of the swollen stem, 

 epitomizes the course of practically all of the hyphse studied in the 

 several longitudinal sections. The hyphse enter the longitudinally 

 directed wood tracheids through the path of least resistance, viz., 

 through the membrane of the bordered pit (figs. 24, 24a, 25, 26). 

 In several instances this mode of exit and entrance is clearly trace- 

 able in the sections. By following the course of a hypha through 

 the lumen of a tracheid it is found suddenly to dip down at the 

 pointed extremity of the tracheid, opposite to the last bordered pit, 

 and after disappearing from focus it again appears in another 

 tracheid. By carefully focusing it is demonstrated that the liypha 

 passes through the bordered pit, and after taking a U-shaped 

 bend it appears again on the oi'iginal level in another tracheid (Hg. 

 22). 



The mycelium does not show any relationship to the nuclei of 

 the host cells, such as has been demonstrated to be the case witli the 



" Farlow found in O. macropus the mycelium in the leaves where 

 there are haustoria [sic] which enter the' parenchymatous cells. The 

 fact that the mycelium grows in the leaves and not in tiic slt-m may 

 account for this difference in growth. 



