364 Wisconsin Academy of Sciences, Arts, and Letters. 
nuclei show no change in structure until some time after the 
germination of the spore. As soon as the first hypha has several 
branches, one observes the first changes in the nuclei as de¬ 
scribed below. 
A nucleus in the resting spore and during early stages after 
germination consists only of a homogeneous, deep-staining, ap¬ 
proximately spherical body which I consider to be chromatin in 
nature. Its surface is undoubtedly membranaceous, although 
no membrane is differentiated. With the triple stain this body 
stains deeply with the safranin while the surrounding cyptoplasm 
stains orange. The first change that occurs in such a nucleus is 
the swelling of the chromatin body accompanied by the formation 
of a vacuole within it. In some instances the chromatin becomes 
distributed for a time in the peripheral zone. With further growth 
of the vacuole the chromatin becomes separated at one or more 
points. If separated at one point, the chromatin may present a 
somewhat crescent-shaped optical section (fig. 2f). On the other 
hand, it may be separated so as to present a somewhat horseshoe¬ 
shaped section with a chromatin body in the opening of the horse¬ 
shoe (fig. 2b). Usually the chromatin substance is separated into 
from three to six bodies, as the growth of the vacuole progresses 
(figs. 2a, 2c, and 2d). Figure 2 illustrates the distribution of such 
nuclei associated with vacuoles from a hyphae in the substratum of 
a three-day-old culture. 
The question naturally arises in this connection concerning the 
nature of the membrane surrounding the nuclear vacuole. The 
vacuole evidently originates below the surface of the chromatin. 
But as soon as the chromatin is separated sufficiently at any point 
a thin membrane remains surrounding the vacuole; the membrane 
does not stain with the safranin as does the chromatin but stains 
more as does the surrounding cytoplasm. This may be due to the 
fact that it is so thin as not to appear differentiated from the sur¬ 
rounding cyptoplasm, but I am inclined to believe that, while the 
membrane originates within the chromatin, its composition be¬ 
comes changed and so differentiated from the chromatin. 
The above-described vesicular body has undoubtedly been inter¬ 
preted by most workers as the nucleus. Since, as I shall point out 
later, such a vesicular body functions as a single structure of the 
protoplasm at certain stages in the life history of the plant, per¬ 
haps it would not be incorrect to consider it a nucleus. However, 
on account of its behavior in connection with division and distribu- 
