666 
Notes . 
dimensions ; thus one nucleus measured 0-3 mm. long and 0-2 mm. 
broad. Sometimes these nuclei break up simultaneously into a 
large number of small nuclei, sometimes they become constricted 
in the middle, and after drawing out into the shape of an hour- 
glass divide into two equal daughter-nuclei. In another form of 
a direct division the nucleus forms a large number of bud-like 
projections from its surface which become separated from the parent 
nucleus. Ring-shaped nuclei were also often met with, which divide 
into two, three, or four daughter-nuclei according to the number of 
places in which the ring becomes attenuated. 
It was in the smaller nuclei I observed transition-forms between 
direct and indirect fission. In these cases the nucleoli disappear and 
the nuclear thread breaks into a number of chromosomes ; but without 
the nuclear membrane dissolving or the formation of a nuclear plate, 
the nucleus becomes constricted across the middle so that it appears 
dumbell-shaped. The piece connecting the two daughter-nuclei 
usually lies more to one side than the other, and beside it is formed 
an apparently normal achromatic spindle. The solution of the 
nucleoli and the persistence of the nuclear membrane during these 
direct divisions prior to the formation of the spindle, supports the 
view that this latter structure is in part derived from the nucleolar 
substance. In these divisions I could not observe a longitudinal 
fission of the nuclear thread. 
It is to be noted that the direct as well as the transition-forms of 
nuclear division were, in the cases observed, found in groups among 
nuclei exhibiting normal karyokinetic figures, from which we may 
conclude that the abnormal forms are not the result of imperfect 
fixing, and also that the same stimuli give rise to both kinds of 
division. Nearly all these forms of nuclear fission have been observed 
in animal cells, but so far as I am aware, they have not been recorded 
as occurring in plants. H. H. DIXON. 
Trinity College, Dublin. 
FURTHER INVESTIGATIONS ON SPORE-FORMATION 
IN FEGATEX1I1A CONICA. — I have already (page 489 et seq.) 
described the chief points connected with the nuclear divisions in this 
plant. Since that paper was written my plants have fruited again, 
and as a large amount of material has rendered it possible to fill up 
some of the gaps existing in my previous account, I now briefly 
summarize the new results. 
