THE TRANSLOCATION OF PROTOPLASM 155 



mycelia of the Mucorineae might be formed like the wall of the 

 columella, but a special investigation carried out with the help of 

 my research assistant, Mr. C. C. Neufeld, has shown that the septa 

 in the mycelium are developed in the same way as those of Spirogyra, 

 i.e. by the closing-diaphragm process carried to completion (Fig. 78, 

 A-E). In Rhizopus nigricans a septum starts as a circular rim and 

 grows inwards toward the centre of the cell. During this process 

 protoplasm has been observed passing through the diminishing pore 

 from one cell to the next (Fig. 79, B). However, the pore, just as 

 in Spirogyra, quickly becomes closed up (C), so that a mature 

 septum of R. nigricans differs from a mature septum of one of the 

 Higher Fungi in being entire and imperforate instead of having a 

 pore at its centre. In R. nigricans protoplasm has never been seen 

 streaming through the centre of a mature septum and this, doubtless, 

 is due to the fact that such a septum has no central pore. Soon 

 after its formation, a septum in an evacuating mycelium of R. nigri- 

 cans becomes concavo-convex (D and E), owing to the turgidity of 

 the terminal cell having become greater than that of the subterminal 

 cell. At the moment when the terminal cell dies, the subterminal 

 cell presses the septum into the terminal cell (F), and thus the bulge 

 in the septum becomes reversed in direction. When one of two cells 

 in the mycelium of R. nigricans is killed or dies, there is no instan- 

 taneous formation of a plug in the middle of the septum. The 

 absence of a pore in the septum renders the formation of such a plug 

 unnecessary. If we accept the view that a mature septum in the 

 mycelium of R. nigricans is imperforate, the fact that septa are 

 formed only in an older evacuating mycelium and only where they 

 •cut off a piece of the mycelium which has become emptied of its 

 massive labile protoplasm from a piece which has an abundance of 

 such protoplasm becomes intelligible : the septa in this species are 

 never formed in places where they would hinder the flow of the 

 labile protoplasm from smaller ultimate hyphae into the larger 

 hyphae or from these larger hyphae into the sporangiophores and 

 sporangia. 



In Rhizopus nigricans, as the labile protoplasm in an evacuating 

 mycelium passes out of a terminal hypha or system of hyphae 

 (cf. Figs. 7G and 79), the place of the labile protoplasm is taken by 



