204 Farmer and Dig by.—On the Cytological Features exhibited by 
may be, the facts cannot be without importance as we gradually arrive at 
a position which may enable us to formulate a coherent theory of the 
mechanism which is responsible for the distribution of the chromosomes 
to the daughter-nuclei at mitosis. 
Before considering the various aberrant features which the chromo¬ 
somes of P. Schneideri exhibit during the heterotype mitosis, we may pro¬ 
ceed to describe the mode of spindle-formation in these cells. As in the 
common polypody, the spindle is usually quadripolar instead of bipolar. 
It is, however, never so well developed as in the parent species (cf. Figs. 26, 
27, with 16, 17), and this fact is to be correlated with the relatively poor 
amount of cytoplasm which, as we have already said, is present in the cells. 
Probably the abnormal character of the nuclear metabolism may also act as 
a contributory cause. The first indications of spindle-formation are to be 
seen during the later stages of the thick spireme, just when what we have 
elsewhere termed the ‘second contraction’ is setting in. The fact that 
sometimes its inception may apparently be deferred to even later stages is 
perhaps to be attributed to the difficulty of recognizing the earliest stages 
in cells that under any circumstances do not form the achromatic structures 
as distinctly as in the majority of allied forms. 
The kinoplasmic differentiation around the nucleus can be made out, 
though often with difficulty, at earlier stages. Then there occurs a similar 
aggregation of the chromatic linin such as we have described above for the 
other ferns. The chromatic linin forms a bunched mass (Figs. 26, 27), often 
very prominent and striking, just beneath the nuclear wall, and at several 
spots. The kinoplasm on the outer side of the nucleus, at places exactly 
corresponding to these aggregations, is repelled, or at any rate diverges 
there, from the surface of the nucleus. It differentiates into spindle fibres 
which, though feebly developed, ultimately traverse the cytoplasm to the 
periphery of the cell, and end in denser masses of protoplasm just beneath 
the cell-wall. Sometimes there are clusters of granules at these spots, but 
the cytoplasm also contains other granules distributed in its mass. The 
appearance of the fibres in surface view is often very remarkable, as is 
shown in PI. XVIII, Fig. 29. It may happen, however, that the spindle is 
not quadripolar but bipolar at these stages, though this is not of frequent 
occurrence. The nuclear wall remains intact till diakinesis, and at this stage 
the quadripolar arrangement of the chromosomes is often very striking. 
At other times the chromosomes are apparently grouped in three clumps 
(Fig. 32), two being smaller than a prominent central group. 
As the wall of the nucleus breaks down, the spindle immediately becomes 
bipolar, but the three or four chromosome clusters may persist. Such cases 
lead to very irregular figures, as the two smaller sets move at once 
towards the poles, whilst the more central group or groups take some time 
to point off to their respective destinations. 
