NUCLEAR BEHAVIOR IN PROMYCELIA 
41 
chromatin reticula are hard to demonstrate. I find no evidence of 
disintegrating nuclei in any of the spores. 
The normal germination of the aecidiospore consists in the pushing 
out of a germ tube into which the protoplasmic contents of the spore 
passes. See figure 5. As the nucleus travels out into the germ tube 
it becomes elongated, figure 6. This nucleus soon divides, figure 7, 
producing two nuclei which may again divide immediately as shown in 
figure 8. The two nuclei that are the product of the first division may 
round up as shown in figure 9 and may even become separated by a 
cross wall before the second division occurs. Figure 10 shows a spore 
containing two nuclei and producing a germ tube. This suggests 
that here as in Endophyllum sempervivi according to Hoffmann the 
first nuclear division may occur in the spore. 
Nuclear division, as noted, is sometimes followed immediately by 
cell division, figure ii, but in other cases the four nuclei of the pro- 
mycelium may be present before cross walls are formed. There is soqie 
evidence that these cell divisions take place by constriction, as has 
been reported in other rusts (9 and 16), but I have not studied this 
point especially. The second nuclear division is soon followed by cell 
division giving normally four cells that are filled with protoplasm 
and contain one nucleus each, together with a stalk cell which is with- 
out a nucleus. The stalk cell is either empty or contains a very small 
amount of protoplasm at or near its upper end. We have here a 
case in which a cell is cut off which contains no nucleus and may or may 
not contain protoplasm. When protoplasm is present it is massed at 
the upper end of the cell leaving not even a vacuole and primordial 
utricle in the lower end. I have occasionally observed promycelia 
that are composed of more than five cells. Such promycelia, however, 
never produce more than four sporidia and when they are stained show 
a nucleus in only four of their cells. Brefeld (3) has observed a similar 
cutting off of functionless cells in the promycelia of Tilletia Caries, 
Ustilago Maydis and other forms. 
The sterigmata arise as pointed protrusions from the nucleated 
cells of the promycelium. They are generally though not always 
produced near the distal end of the promycelial cell. After reaching 
a length of from fifteen to twenty microns the extreme end of the ste- 
rigma begins to enlarge. Thus the sporidium arises through the enlarge- 
ment of the end of the sterigma. At first this enlargement is almost 
spherical, but it soon takes on the shape of the mature sporidium. 
