in the Hymenomycetes . 51 1 
divides into two, probably by a process of karyokinesis similar 
to that observed in the basidium, but as I have not been able 
to make out these points as clearly as I should like, I will 
reserve the discussion of these observations for a future paper. 
In conclusion it may be useful to summarize briefly the chief 
facts made out in this investigation. 
Summary of Results. 
1. The young basidia of Agaricus stercorarins and A. mus - 
carius contain a single nucleus formed by the fusion of two or 
more pre-existing nuclei. 
2. The structure of the nucleus is similar to that in the 
higher plants ; it possesses a nuclear membrane, nucleolus, and 
granular network. On staining with carmine and nigrosin 
the network becomes blue, the nucleolus a deep reddish 
purple. 
3. The division of the nucleus is karyokinetic, resembling, 
generally, that which takes place in the higher plants, but with 
slight differences of detail. The chromatin-network breaks up 
into segments, which accumulate at one side of the nucleus. 
The nucleolus begins to dissolve, and at the same time the 
chromatic elements begin to stain more deeply than before. 
The nucleolus does not disappear entirely until the division is 
nearly complete. A spindle-figure is formed in connexion 
with the chromatic elements ; the latter divide into two groups, 
which pass along the threads to the poles of the spindle. 
4. The chromatic elements fuse together at the poles of the 
spindle ; a new nuclear membrane appears around each 
daughter-nucleus, and a new nucleolus and nuclear network 
become differentiated. 
5. The daughter-nuclei divide in the same manner as the 
parent nucleus. 
6. The four nuclei thus produced pass at once to the base 
of the basidium and come into such close contact as to appear 
fused together. After a time they separate again, pass to the 
apex of the basidium and place themselves immediately at the 
base of the sterigmata. 
