Poke 
= 
ee 
THE NUCLEUS.—CELL-SAP. 27 
is differently characterised, and defined as the onter thin homo- 
geneous layer or ectoplasm of the protoplasm. This is the sense 
in which it was essentially understood by Mohl. 
3. Tue Nuctevs, which exists in all the cells of the higher 
plants, and is absent from only a few of the lower forms, is 
differentiated from the surrounding protoplasm as a denser por- 
tion of the same substance (figs. 37, c, and 38). It appears to 
consist of a homogeneous matrix termed achromatin, in which 
a network of fibrille (chromatin) is contained. It usually 
presents a more or less rounded outline, and contains one (figs. 
Fic. 43. Fic. 44. 
Fig. 43. Semi-diagrammatic longitudinal section of an old and stout portion 
of Ceramium rubrum, showing continuity between the protoplasmic con- 
tents of the axial or central cells, a, a, at their ends; and laterally with 
the cortical cells, b, by protoplasmic threads, and also that of the corti- 
cal cells inter se by threads radiating from the central mass in each 
cell, After T. Hick. ——Fig. 44. 1. Endosperm cell of Sirychnos Ignatia, 
swollen up in water, showing threads of protoplasm (plasmolytic threads) 
running to the cell-wall, p. 2.The lumen of two endosperm cells of 
Strychnos Nux-Vomica, showing plasmolytic threads passing into intra- 
mural ones, thus demonstrating continuity. 3. Plasmolytic threads from 
endosperm of S. Jgnatia. 4. Top of a branch of Callithamnion sv., show- 
ing cell junctions and continuity of protoplasm. After Le M. Moore. 
37, c, and 38), or more (fig. 39, k’, k’), much smaller bodies, 
called aueleoli. It is always situated in, and more or less en- 
closed by, the protoplasm, as we have already seen, and never 
lies loose in the cell cavity. Itis, when present, the most vitally 
active part of the living substance or protoplasm. (See also 
‘Formation of Cells,’ in the Physiology of Plants.) 
4, Tue CELL-sap is the watery fluid which is found in the 
interior of the cell ; it contains dissolved or suspended in it ali 
those food materials which are necessary for the life and growth 
