286 Allen . — The Early Stages of Spindle- Formation 
activity of the kinoplasm in the absence of undifferentiated 
dynamic centres. In spite of numerous accounts of central 
bodies, the great weight of evidence now seems to be against 
their existence in the Seed Plants, if we except the still 
disputed case of the ‘ blepharoplast.’ A full resume of the 
centrosome discussion has lately been published by Strasburger 
(’00), who has still more recently (’01) applied to the pollen- 
mother-cells of Asclepias and Cynanchum , with negative 
results, all the methods used for the demonstration of the 
central bodies in animal tissues. The observations and ex- 
periments of Hottes (reported by Strasburger, ’00) and of 
Nemec (’99 d, ’ 01 ) indicate that kinoplasmic or nucleolar 
granules or masses may often appear at or near the spindle- 
poles, and that their occurrence is favoured by certain stimuli, 
as, for instance, subjection to low temperatures. Demoor 
(’ 95 ) also finds that ‘ centrosomes ’ are made visible by 
cooling. 
The only history of a multipolar spindle so far completely 
worked out among the Pteridophytes is that of the spore- 
mother-cell of Equisetum , described by Osterhout (’ 97 ). He 
finds, just without the nucleus, a blue-staining cytoplasmic 
layer, which becomes fibrous ; the fibres are at first parallel 
to the nuclear membrane, but later take on a radial arrange- 
ment, many of them extending to the plasma-membrane ; 
then they group themselves into a multipolar figure. The 
nuclear membrane disappears, and the extra- and intra- 
nuclear fibres form a continuous system, whose poles fuse in 
two groups, forming a sharply bipolar spindle. No centro- 
somes are present at any stage. The multipolar origin of 
this spindle is corroborated by Nemec (’98 #) ; but Campbell 
(’ 95 , p. 427) finds directive spheres present in the divisions of 
the spore-mother-cell, and describes no multipolar stage. 
Smith (’00 a) notes that the spindle in the microspore-mother- 
cell of Isoetes appears to have a polycentric origin. In the 
spore-mother-cells of Osmunda , he (’00 b) describes the for- 
mation of a spindle from two extra-nuclear polar caps — a 
‘ multipolar diarch ’ origin. Occasional tripolar figures he 
