in the Pollen- Mother- Cells of Larix . 297 
Conclusions. 
The facts observed in the pollen-mother- cell of Larix 
seem conclusive as to the continuous presence in the cyto- 
plasm, from the very early prophases, of a distinct fibrous 
system, which, after a series of rearrangements and changes 
of position, becomes, in conjunction with another set of fibres 
of nuclear origin, the karyokinetic spindle. A careful study 
of the preparations leaves no doubt, I think, that the fibres of 
the reticulum first seen actually become rearranged into 
a radial system, that this in large part passes into a close 
extra-nuclear felt, and that the fibres of this felt become 
eventually the contribution of the cytoplasm to the com- 
pleted spindle. It is impossible to determine in the mature 
spindle that any special portion is derived from the cytoplasm 
or from the nucleus ; but each source clearly furnishes an 
important part. It follows that the active spindle-forming 
substance, kinoplasm, may first appear, in fibrous form, either 
in the nucleus or in the cytoplasm ; and we may infer that 
the place of origin of the spindle-fibres, whether nuclear or 
cytoplasmic, or, as in the present case, partly nuclear and 
partly cytoplasmic, depends upon the conditions obtaining in, 
and the relations between, the nucleus and cytoplasm of the 
cell concerned. The facts accord with this inference ; spindles 
of intra-nuclear origin sometimes occur in connexion with an 
unusual size of the nucleus, as in the generative cell of Zamia 
(Webber, ’01), or where there is a paucity of cytoplasmic 
kinoplasm, as in instances cited by Strasburger (’00) in young 
anthers and nucelli of Lilium and in the growing point of 
Viscum ; and a greater proportional supply of extra-nuclear 
kinoplasm may result in spindle-formation such as Nemec 
finds in many vegetative cells, where an extra-nuclear bipolar 
spindle is completely formed, save for a short equatorial 
portion, while the nuclear membrane is still intact. 
But in spite of the range of variation which has been found 
in this and in other respects, I think that we may venture to 
present tentatively, in a general outline, the essential steps in 
x 
