SPECIAL NUCLEAR PHENOMENA. 49 



The metamorphosis of the polar aster in Phyllactinia and Brysiphe 

 cichoracearum is entirely similar to that in Brysiphe communis. In 

 view of the above-described facts as to the connection between chro- 

 matin and central body at other stages, it is interesting to note that in 

 the protrusion of the nuclear beak the same condition comes most strik- 

 ingly to view, ^he beak is not merely an extension of the nuclear 

 membrane, but the chromatin is also pulled out as slender strands in the 

 beak and maintains its connection with the central body through the 

 whole process of the delimitation of the spore. This is very clearly 

 shown in both Erysiphe and Phyllactinia (figs. 70-78). 



The central body on the apex of the beak is very broad and flat in 

 Phyllactinia (fig. 72) . Its diameter is apparently greater than that of the 

 outer portion of the beak. I have occasionally found cases in which the 

 central body had divided at the end of the beak and the fibers were also 

 separated into two systems (fig. 80). Whether this condition would be 

 followed by normal spore formation I have not determined. It shows the 

 capacity of the centers to divide and seems to indicate that such division 

 separates the fibers into two groups without splitting each fiber. 



The process by which the beak is fomied on the nucleus is not easy 

 to understand. I have elsewhere discussed (38) the possible methods 

 by which such a beak-like elongation may be pulled or pushed out from 

 the surface of the nucleus. ' My observations on Phyllactinia and 

 B, cichoracearum incline me more strongly to the view that it is formed 

 by the activity of the aster rather than by any spontaneous change of 

 form in the relatively inert nuclear mass. 



In B. cichoracearum it seems plain, as I found was the case some- 

 times in L,achnea and Pyronema, that in some cases, at the time of the 

 formation of the beak, the center and aster may be in close contact with 

 the plasma membrane of the ascus (figs. 69, 73, 74), just as is quite 

 regularly the case with the supernumerary nuclei (figs. 70, 73, 81). 

 The folding over of the rays may begin while the centers are in this 

 position and may seem to be a result of the flattening of the aster 

 against the membrane of the ascus (figs. 73, 74). 



In Phyllactinia the beaked nucleus and aster seem much more com- 

 monly to lie free in the cytoplasm from the start (figs. 70, 71, 72). 

 Occasionally, even when the center is quite distant from the plasma 

 membrane, a broad depression is found in the latter just opposite the 

 center, as if the astral rays were attached to it and by contraction had 

 pulled it away from the cell- wall (fig. 71). In the later stages in all 

 cases the whole system is found lying free in the cytoplasm and gener- 

 ally at some distance from the wall of the ascus. It is quite possible that 



