34 INTRODUCTION. * 
the aster is converted into a hollow cone whose apex is the centro- 
sphere. Neighboring radiations unite and grow rapidly in length, at 
the same time bending back toward the nucleus in a manner resem- 
bling the spray from a fountain. An optical section of this stage is 
shown in Fig. 12,C. With further growth the kinoplasmic rays give 
rise to a sort of bell-shaped or half-ellipsoidal structure whose center 
is occupied by the nucleus and whose pole is formed by the centro- 
some (Fig.12,D). Near the centrosome the fibers have already formed 
a continuous but extremely thin layer, the plasma membrane, separat- 
ing the cytoplasm of the spore from that of the ascus. At the edge of 
Fic. 12.—Free cell-formation in ascus of Erysiphe communis. 
* 
A, nucleus with centrosphere. 
B, development of nuclear beak. 
C, polar radiations extend outward and backward as spray from a fountain. 
D, formation of plasma membrane from end of beak outward, and continued growth of kinoplasmic 
fibers backward, 
E, F, meeting of fibers at opposite end of ellipsoidal spore and establishment of a complete plasma 
membrane delimiting spore-plasma from remaining plasma of ascus.—(After Harper.) 
the bell the radiations end as free fibers, continuing their growth, how- 
ever, in a direction corresponding to the periphery of the ellipsoid 
(Fig. 12, E). Finally these fibers meet in a point which is directly 
opposite the centrosome, and unite end to end and laterally. The for- 
mation of the plasma membrane continues, so that eventually an ellip- 
soidal or oval cell is delimited from the cytoplasm of the ascus by 
a complete plasma membrane (Fig. 12, F). At first the plasma 
membrane is thicker near the centrosome, but later its thickness be+ 
comes uniform throughout. 
