380 Mr M*Lean, Amitosis in the Parenchyma of Water-Plants. 
Amitosis in the Parenchyma of Water-Plants. By R. C. M°LEan, 
B.Sc., Lecturer in Botany at University College, Reading. — 
(Communicated by Professor Seward.) 
[Read 9 February 1914.] 
It is desired to record the observation that the amitotic or 
direct process of nuclear division commonly occurs in the cortical 
parenchyma of aquatic angiosperms. 
The phenomenon was first noticed in Myriophyllum proser- — 
pinacoides and afterwards in Hippuris vulgaris. This suggested 
that it might be characteristic of aquatics, and several other 
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species, both Dicotyledons and Monocotyledons, were investigated 
from this point of view, with the result that a wider distribution 
of the phenomenon was discovered than had been presupposed 
to be the case. The transverse section of the stem-internode of 
Myriophyllum exactly resembles a wheel in its general outline. 
The hub is formed by the stele, which consists of a central mass 
of pith, around which lie a small number (six or seven) of vascular 
bundles which are simply collateral, neither xylem nor phloém 
being strongly developed, while around all this lies a well-marked 
endodermis. The cortex consists of three parts, an inner zone, 
enclosing the stele, an outer zone immediately under the epidermis, 
forming the rim of the wheel, and an intermediate zone which 
consists of long strands of parenchyma—the spokes of the wheel, 
which separate the large air-lacunae from one another. It is in 
the innermost zone, that immediately surrounding the stele, that 
amitosis 1s most easily observed, although it has been seen in the 
outer cortical zone and in the trabeculae between them as well, 
only more seldom. In these latter cases the nuclei show the 
common spheroidal form. In Hippuris the stele is central as in 
Myriophyllum, but the cortex shows only one zone, consisting of a 
wide zone of reticulate trabeculae surrounding numerous large air- 
lacunae. Of all the plants so far examined, Hippuris shows the 
phenomenon more clearly and more widely spread in the tissues 
than any other. 
In order to see the nuclei well it is best to use fairly thick 
sections, transverse or longitudinal, which include at least the 
thickness of one whole layer of parenchyma cells. These may 
then be observed unstained in glycerine, or stained carefully with 
carbol-fuchsin, acetic acid, methyl-green, or other direct acting 
nuclear stain. If the chloroplasts take the stain it will be difficult 
to distinguish the nuclei among them. 
The general distribution of amitosis in the tissues follows the 
general distribution of growth. Cells showing it are commoner in 
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