382 Mr M*Lean, Amitosis in the Parenchyma of Water-Plants. 
they twist round one another. Apparently the separation of the 
nuclei from one another after division is very slow. Large and 
conspicuous nucleoli are always present, either one or, occasionally, 
two in each nucleus. The nucleolus sometimes causes a bulging-— 
out of one side of the fusiform nuclei. 
Stages in the actual separation of the two daughter-nuclei may 
be observed. No constriction is formed, but the process proceeds 
like the longitudinal fission in the Flagellata, from end to end, by 
gradual separation of the two daughter-nuclei. Amitosis is the 
only form of nuclear division which has been recognized in the 
tissues investigated, and from its exceeding frequency in the 
constituent cells it may be inferred that it is the only form 
occurring there. 
Besides the two plants—Myriophyllum and Hippur1is—men- 
tioned above the following plants show the same phenomena in 
their cortical tissues. 
Dicotyledons Monocotyledons 
Trapa bifida. Elodea canadensis. 
Jussieula sp. Potamogeton lucens. 
(Hippuris). Limnocharis sp. 
(Myriophyllum). Aponogeton sp. 
All the above are aquatics, but two land plants have also been 
noted as showing resemblances to the aquatics in the above - 
respects. These are Dionewa muscipula and Polypodiwm «reordes. 
The first is of course a marsh plant, but the second is an epiphyte, 
and as far removed from an aquatic as may well be. This suggests 
that the phenomena of amitosis in plants may well be much more 
widespread than has hitherto been supposed, and opens up a new 
field for thought in regard to its theoretical importance in cytology. 
It is generally admitted that amitosis represents only a fragmen- 
tation rather than a qualitative division of the nuclear substance, 
and that the complex phenomena of mitosis are adapted to the 
segregation of the histogenetic characters resident in that sub- 
stance. Mitosis should therefore be the characteristic form of 
nuclear division in tissues which are undergoing ontogenetic 
growth. If, however, growth continues in a tissue which has 
already become fully differentiated, it is hard to see what further 
need there is for mitosis to take place. Amitosis may therefore 
be the constant form of nuclear division between sister-cells in all 
fully differentiated tissues which remain alive and continue to 
grow in bulk, although this does not preclude the possibility of its 
occurrence in meristematic tissues as well. 
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