120 KANSAS UNIVERSITY QUARTERLY. 



walls independently of any natural openings. In fig. i the mycelium 

 is seen to contract as it penetrates the wall, and to emerge into the 

 cell with about half its former diameter. In the same figure a fila- 

 ment starts out suddenly, follows the contour of the cell for a short 

 distance, and terminates without manifesting any disposition to pene- 

 trate the wall. Similar occurrences are seen in figs. 2 and 4. Cases 

 of this kind are not infrequent. They seem to result from branches 

 that have been confined between the walls of contiguous cells, but 

 have at last made for themselves a passage into the cell. In fig. 2 the 

 mycelium is again seen to contract as it passes through the upper wall. 

 In the lower portion of the figure the mycelium has bulged out before 

 penetrating the wall, as though new material were added to the grow- 

 ing point faster than it could penetrate the wall. Contraction has 

 taken place, however, while penetrating the wall, and afterwards the 

 filament has grown considerably thicker and formed a shoulder on the 

 inner surface of the cell. In fig. 3 penetration has taken place at one 

 of the natural openings, although on both sides of the wall the filament 

 is much larger than the opening. ■ After entering the cell the filament 

 bifurcates, one branch penetrating into an adjacent cell without suffer- 

 ing any change in its diameter, the other evidently becoming lost in 

 the interspace between the cell walls, probably to reappear abruptly 

 at another place similarly to the sudden eruptions in figs, i and 4. 

 The mycelium entering the cell from above, in fig. 4, does not have its 

 diameter materially altered ; it undergoes change in direction, how- 

 ever, and appears to cause the cell wall to protrude on both sides. 

 As the filament leaves the cell it is abruptly reduced to almost one- 

 third its former diameter, and soon terminates, after sending off short 

 branches. In figs. 5 and 6 the plasticity of the growing point is illus- 

 trated. Here, for some reason, the penetration of the cell wall was 

 not effected and the accretions of new material have become heaped 

 up on the inner surface of the cell wall. These, and other sections 

 which I have examined, appear rather to bear witness for the theor}^ 

 of the perforation of the cell wall by means of a ferment secreted by 

 the fungus, than for the theory of mechanical puncture. The sudden 

 emergence of a filament after evident meanderings between cells, does 

 not occur under the proper conditions, it seems to me, for the punc- 

 ture of the wall at a certain point by pressure. If the wall is punctured 

 mechanically, the faster growth at the top takes place the quicker the 

 perforation would be accomplished. On the other hand, rapid growth 

 of the filament would not necessaril}^ produce a correspondingly rapid 

 perforation of the cell wall if the perforation were caused by a fer- 

 ment, and we would find at times such accumulations of plastic mate- 

 rial as those shown in figs. 2, 5, and 6. While mycelial branches 



