l62 



RESEARCHES ON FUNGI 



which have become isolated from one another by the death of one 

 or more intervening cells become re-united {cf. Figs. 71 and 72, 

 pp. 138 and 139) ; for, shortly after a septum has come to separate 

 a living from a dead cell, it is frequently used as a point of departure 

 for the growth of a new hypha (Figs. 69 and 70, pp. 135 and 137). 



Fig. 81. — Rhizopus nigricans. Successive stages in the formation of a septum at 

 the base of a hypha which has evacuated most of its protoplasm, represented 

 in optical median-longitudinal sections. A, a septum is about to be formed 

 near the end of the vacuole ; the vacuole in the branch -hypha is enlarging and 

 pushing the protoplasm slowly toward the main hypha ; the two larger arrows 

 represent the direction of movement of the labile protoplasm as a whole, while 

 the smaller arrows indicate that irregular longitudinal rotatory movements are 

 going on in the protoplasm bounding the vacuole. A was drawn at the zero 

 of the time-scale, and the time in minutes at which each of the other stages was 

 drawn is indicated above each of the drawings B-F. The total time in which 

 all the changes were observed was 40 minutes. B, the septum, in the form of 

 an annular ingrowtli from the lateral wall of the branch-hypha, has begun to 

 form. C, the septum is more than half-formed. D, the septum is almost 

 complete ; particles of protoplasm are still passing through the pore in the 

 direction indicated by the arrow. E, the septum is now complete ; its pore 

 has been completely closed up. The septum has taken 20-25 minutes to form. 

 F, as a result of the continued expansion of the large vacuole, the septum has 

 been pressed forward, so that it now bulges toward the main hypha. Drawn 

 by A. H. R. Buller and C. C. Neufeld. Magnification, 1007. 



Time taken for the Formation of a Septum. — The formation of 

 a septum as an annular ingrowth from the lateral wall of a hypha 

 takes a certain time. The formation of particular septa from their 

 first beginning to completion was watched under the microscope, 

 and it was found that the time taken for the formation of a septum, 

 on the average, is : in Rhizopus nigricans, 20-25 minutes (Fig. 81) ; 



