146 Lloyd Williams . — Studies in the Dictyotaceae. 
that the quantity of chromatin is not sufficient to form a continuous 
spirem.’ This, however, is a mistake. It would be hard to find a more dis- 
tinct spirem than this, or one more interesting in its development. Many 
hundreds of them have been studied, and in some material they are far 
more numerous than spindles, showing that they persist for a considerable 
time. The main features of the spirem stage in Dictyota are so constant 
that no one after seeing the synapsis could possibly call it an artefact. 
After completing the work on Dictyota I began to study the cytology 
of Padina. This plant was found to agree with Dictyota in all the principal 
points, while it presented the great advantage of having the various stages 
sorted out as it were. In Dictyota the sporangia are isolated and the 
various stages are generally mixed up in a haphazard fashion. Thus 
the finding of any particular stage is a matter of chance, and in order 
to fill up some of the gaps several thousand sections have been examined. 
In Padina , however, the sporangia are collected together in concentric 
bands on the fan-shaped thallus, and in these bands many hundreds are so 
closely crowded together as to be in actual contact. Furthermore, all the 
primary sporangia in any one band are approximately in the same stage. 
Thus the first band behind the apical region is frequently found to have all 
the nuclei in the spirem stage, while the older band behind this has the 
sporangia in various stages of division. In very old sori, where there 
has been liberation of spores, new sporangia are initiated ; here the uni- 
formity above spoken of does not obtain. 
The failure to recognize this stage is probably due to the fact that 
the tetrasporangia in Mottier’s plants were too old, for it is a striking 
peculiarity of Dictyota and Padina that the spirem appears as soon as the 
mother-cell has been separated and while the sporangium is still young 
and small ; it then disappears, and the nucleus assumes the appearance 
of the resting stage. In the preparation for this mitosis there are then 
three well-marked stages : (1) A very precocious spirem, which lasts a con- 
siderable time and goes through several interesting changes. (2) A reti- 
culum stage, which is exactly like that of rest. It is with this that Mottier’s 
studies commence, and his Fig. 1 comes between Figs. 14 and 15 of 
this series. (3) A prophase stage which is passed through somewhat 
quickly. 
The Synapsis Stage. The spirem is now very long, thin, and deeply 
stained. It is closely coiled up into one or two clumps of angular 
loops (Figs. 8 and 9). The two knots appear closely pressed against 
the nuclear membrane, one opposite each centrosphere. The centrosome 
and radiations are still very indistinct, those shown in Fig. 8 being the best 
observed. The nucleus is very large, but the membrane is thin and 
ill-defined. The knot is so pressed against the membrane that it is 
often difficult to decide whether the spirem is entirely within it, and it 
