212 A. B. MACALLUM. 
than they are in the living cell, for, as a rule, they only 
partially occupy the cavity in which they lie (figs. 17 and 19). 
I have in some cases isolated them from their nuclei in the 
glycerine and sulphide mixture, and the greenish reaction 
which they gave could, therefore, not have been due to the 
iron of a compound which diffused from the chromatin 
elements into them. When the sections were treated with 
sulphuric acid alcohol and subsequently with the acid ferro- 
cyanide mixture and the eosin solution, the result was usually 
that of which fig. 42 is a representation, These nucleoli stain 
intensely with eosin, which also colours very slightly the chro- 
matin network, the blue of the latter thereby becoming violet, 
but after being thoroughly washed in alcohol the bright blue 
colour returns; while this treatment makes no difference in 
the intensity of the stain in the nucleolar bodies. These 
effects are most distinctly observed when the diaphragm of the 
Abbé condenser is removed from the field, in which case it is 
possible to see the most minute of the nucleolar elements, 
a device that is necessary when the nuclei of ordinary paren- 
chyma cells are under examination. 
In the second class are those nucleolar elements which may 
be found in the cells of the nucellus, and which are composed 
of chromatin, since they give a deep iron reaction after the 
employment of any of the methods of treatment for liberating 
the element, and since, also, they stain in every respect like the 
chromatin threads. They usually occupy cavities in the nuclei 
like those which contain the eosinophilous nuclei last described. 
I regard these as reserve masses of chromatin deposited in the 
nuclei engaged in the formation of chromatin, which eventu- 
ally is transferred to the cells of the endosperm. To this 
subject I propose to refer again. 
Nucleoli of the third class are to be found in the nuclei of 
the embryo-sac (fig. 44, a and 6). They are not present in 
the mitotic nucleus, but in the retrogressive stage they appear 
on the course of the filaments as spherical elements enclosing 
one or more refracting corpuscles and containing but a small 
amount of iron, which, however, in later stages, when the fila- 
