502 Harper. — Cell-Division in Sporangia and Asci. 
nuclear division does not precede the pushing out of the germ 
tube as it does in P. crystallinus. The gross structure of 
the plasma is at first typically vacuolar. The vacuoles are 
spherical or flattened against each other, and are entirely 
distinct, each maintaining its outline apparently by surface 
tension of the contained liquid. So soon, however, as the 
germ-tube is pushed out from one side the whole structure 
is transformed, the vacuoles become elongated and fuse, the 
protoplasm is gathered into strands, forming a loose spongy 
net in which streaming is begun at once, and continues as 
long as the cells can be kept under observation without 
suffering from lack of oxygen. This change of the structure 
of the protoplasm can be followed with the greatest ease and 
accuracy, and is entirely similar but in reverse sequence to 
what takes place in the sporangium just before the columella 
is formed. It is apparently a necessary change if streaming 
is to take place in the germinating spore, and is doubtless a 
result of the same influences that lead to those phenomena. 
Figs. 30-32 show the appearance of living spores under 
the 2 mm. apochromatic lens when germinating in a decoction 
of horse-dung. The change from vacuolar to thready structure 
is shown just beginning in Fig. 32. The thicker germ-tubes 
produced when the spores are germinated in a nutrient 
solution instead of water have already been noted by Brefeld. 
The processes of cutting off the sporangium and dividing 
the multinucleated spore-plasma into spores may be sum- 
marized as follows : — 
1. Arrangement of a series of vacuoles in a dome-shaped, 
curved stratum on the inner boundary of the dense spore- 
plasma. 
2. Flattening of these vacuoles and the formation of a cleft 
through them, beginning at the edge of the opening into 
the sporangiophore. 
3. Smoothing of the new plasma-membranes thus formed, 
by turgor of spore-plasma and columella-plasma. 
4. Formation of a columella- wall in the cleft between the 
new plasma-membranes and vacuolization of the spore-plasma. 
