TILLETIA TRITICI 277 



increases in size until it has the appearance shown in C. The apical 

 wall of the vacuole, w, gradually flattens, as shown at D, and then 

 a new septum, s"\ begins to develop, as shown at E. In F the 

 septum has just been formed and, at this stage, it is quite flat. In 

 F we now have four cells instead of three — two, dead, empty, 

 laterally contracted, basal cells a and 6, a highly vacuolated uncon- 

 tracted cell c, and a terminal non-vacuolated uncontracted cell t. 

 The layer of cytoplasm which covers the wall of the cell c is extremely 

 thin, no thicker than the very thin cell-wall and scarcely visible with 

 the microscope ; but there can be no doubt that it is present, for 

 otherwise the cell could not be turgid. 



Undoubtedly, at the stage F in Fig. 135, the promycelium 

 includes two living cells c and t. It therefore seems clear that the 

 septum s'" was formed not at a free surface of the massive proto- 

 plasm of the cell t, but in the protoplasm itself. On one side of the 

 septum, during its formation, there was the massive protoplasm of 

 the cell t, and, on the other side, a very thin layer of protoplasm 

 belonging to the highly vacuolated cell c. It is often stated in text- 

 books that the living part of the promycelium of Tilletia tritici is 

 always unicellular ; but, from the observations just recorded, it is 

 evident that, temporarily at least, it is bicellular. 



The stage F was observed to persist for an hour or more. The 

 septum s'" then very gradually became slightly concavo-convex, as 

 shown at G, thereby indicating that the turgidity of the cell c was 

 diminishing. A little later the cell c died, as was shown by the 



Fig. 135. — The phenomenon of protoplasmic migration and the formation of septa 

 in the protoplasm of a promycelium of Tilletia tritioi. A-J, successive stages in 

 the development of a promycelium which grew in a film of water in a Syracuse 

 watch-glass. Total time of observation, about 3-5 hours. A, a chlamydospore 

 which has produced a promycelium in which the protoplasm has crept forward. 

 There are two septa, s' and s". The basal cells, a and b, are devoid of protoplasm 

 and have collapsed. The terminal cell t is full of protoplasm. B, a vacuole v has 

 now appeared. C, the vacuole is now much larger. D, the massive protoplasm is 

 flattening where it abuts on the vacuole. E, a new septum s'" is being formed in 

 the protoplasm. F, the new septum s'" has been formed and now separates a 

 highly vacuolated living cell c from the living terminal t which is full of prot oplasi 1 1 . 

 G-J, about an hour after F ; the collapse of the cell c. G, the septum s'" is 

 beginning to bulge into the cell c. H, the bulging has attained almost its 

 maximum, the cell c is collapsing, and motile bacteria have been attracted chemo- 

 tactically by the escaping cell-sap. I, the cell c has now completely lost its 

 turgidity and the bacteria are leaving it. J, the bacteria have disappeared 

 and the promycelium is now seen to consist of three short dead basal cells, a, b, 

 and c, and of one long living terminal cell /. Magnification, 750. 



