14 6 RESEARCHES ON FUNGI 



sterquilinus, and C. lagopus, when one focusses with the high power 

 of the microscope on the middle part of a septum, one can see 

 something of the pore. At first one gets the impression that on 

 each side of a pore there is a more or less hemispherical or discoid 

 pad of material which possibly might block up the pore. That this 

 appearance is not due to the cell-wall around the edge of the pore 

 being slightly thickened is indicated by the fact that no such 

 thickening is revealed when hyphae are treated with iodine and 

 chlor-zinc iodine (Fig. 54, B, p. 99) ; and that the appearance is 

 not due to pads of specially dense protoplasm is indicated by the 

 fact that in Rhizoctonia solani it persists even when protoplasm can 

 be seen streaming rapidly through the pore. The " pads " in all 

 probability are due to an optical illusion. Doubtless light impinges 

 on the edge of each pore and the appearance of the " pads " may 

 well be due to the peculiar way in which light passes from the edge 

 of a pore to the eye. 



In Rhizoctonia solani, just as in Pyronema confluens, there can 

 be but little doubt that the movement of the protoplasm along the 

 hyphae is caused (1) by the increase in volume of the vacuoles in 

 certain cells and (2) by the increase in the mass of the protoplasm. 

 In an older mycelium it was observed that the end-cell of a side 

 branch becomes emptied of protoplasm first, and then the penulti- 

 mate cell, and so forth (Fig. 74, B). When a cell has lost nearly all 

 its protoplasm and has come to contain one large vacuole, it suddenly 

 dies. Its turgidity is lost and it contracts in breadth. At the same 

 instant the adjacent living cell pushes forward the dividing septum 

 into the dead cell and plugs up the septal pore. Thus parts of the 

 mycelium become entirely exhausted of protoplasm and thus the 

 streaming of protoplasm along main hyphae to other hyphae which 

 are continuing growth is provided for. 



The emptying and dying of the end-cell shown in Fig. 74, C, was 

 actually observed. At first the cell, which had already evacuated 

 most of its protoplasm, contained nine vacuoles. The walls of 

 protoplasm separating the vacuoles from one another disappeared 

 one by one, so that at length one large vacuole was left (Fig. 74, D). 

 The protoplasm gradually passed out of the cell through the septum 

 until it became reduced to an extremely thin imperceptible layer 



