Beer. — Studies in Spore Development. III. 657 
earlier phase lies in the considerable increase of nucleolar matter which they 
exhibit. Fig. 47 represents a typical example of a spore at this stage, and 
it will be noticed that not only has the number of nucleoli increased within 
the nuclear cavity, but other bodies with all the appearances and staining 
powers of nucleoli also occur in the cytoplasm. 
I have not succeeded in tracing an actual extrusion of nucleolar 
material from the nucleus, but it appears not unlikely that this does take 
place and thus accounts for the origin of the nucleolus-like bodies lying in 
the cytoplasm. 
Very probably the increase in nucleolar matter is associated with the 
active metabolic processes which are taking place within the spore at this 
time in connexion with the elaboration of an exospore. 
Summary. 
A. Premeiotic divisions. 
1. The resting nucleus of the archesporial cells contains a reticulum 
which varies in the degree of its fineness. It may be very delicate and even 
or it may be coarser with small chromatic aggregates upon it. These 
chromatic aggregates, when they occur, show no constancy either in their 
arrangement or in their number. 
2. A spireme develops from the nuclear reticulum by the gradual with- 
drawal of branches and anastomotic connexions, so that first a close 
reticulum is converted into an open one, and then certain lines of concentra- 
tion become apparent. 
3. The spireme is discontinuous from the first. 
4. By further concentration the segments of the spireme shorten into 
the chromosomes, which become arranged upon the equator of the spindle 
which has in the meanwhile developed. The chromosomes are now seen to 
be longitudinally divided. 
5. The daughter chromosomes next move to the poles of the spindle, 
where they become closely massed together. Subsequently they open out, 
and their substance becomes distributed along numerous branches and 
anastomotic connexions which develop between them. It appears to be 
entirely by these means, and without any indications of internal vacuolation, 
that the reticulum of the resting nucleus develops from the chromosomes in 
Equisetum. A nuclear membrane is formed round each daughter nucleus. 
6. A period of complete ‘ rest 5 intervenes between the last premeiotic 
division and the heterotype division. 
B. Meiotic divisions. 
7. Meiosis commences with the gradual withdrawal of many of the 
branches and cross connexions of the reticulum. 
8. Synaptic contraction then occurs, during which the final conversion 
Yy 
