592 J. M. MACFARLANE ON VEGETABLE AND ANIMAL CELLS. 
but is so strikingly exemplified in Chara, of a multinucleolar succeeded by a 
multinuclear condition. 
As we have already seen, it can be said of all the vegetative cells of Chara, 
that sooner or later, after a more or less prolonged period of proliferating 
activity, further multiplication seems impossible, and the cells, while mostly 
increasing greatly in length, all pass into a dormant multinucleolar and not 
infrequently into a multinuclear state. Now, in studying the tissue systems of 
Ornithogalum and Scilla (op. cit., pp. 198-99), exactly the same phenomenon, 
though not so striking in its regularity arrested my attention, causing me to 
conclude “that the nucleolus, or more probably the nucleolo-nucleus is the 
centre of germinal activity, and that. as we pass outwards to the periphery of 
the cell, this reproductive activity becomes less and less. Soon after, when 
studying Chara, I was so struck with the similarity of the process, though on 
a more exaggerated scale; that: an examination of many plants, and a wider 
comparison with other observers, seemed desirable. The result is that in all 
plants thus examined, after cell formation has ceased, continued division of 
the cell contents from the endonucleolus outwards goes on, though in a varying 
degree. Further, not.only does this seem true in the vegetable but also in the 
animal cells, of which more anon. 
But to bring out the phenomenon in Chara more strongly, if we commence 
with a sub-apical cell, this, on division, forms a lower internodal cell, which is 
at once arrested. The upper cell forms the nodal layer of cells which, after 
giving off the cortical and leaf portions, is also arrested. The latter portions 
continue to form many cells till, in the leaf, the three terminal cells and leaf inter- - 
nodes are arrested, and in the cortex the internodes. The cells of the cortical 
nodes and leaf nodes multiply till the former and then the latter are arrested, 
and with their arrest the series of developmental stages is completed. 
We see therefore from this that the general structural peculiarities of | 
Chara result from the different cells being arrested at successive periods, the 
arrest being most complete in the cells as a whole, less so in the nucleus, and least 
of all in the nucleolus and endonucleolus, which, as we have seen, may undergo 
proliferation to a large extent unaccompanied by any change in the nucleus or 
cell as a whole. In this way, two, three, or more nucleoli may soon be formed 
inside one nucleus. This is the usual condition of plant cells which have lost the 
power of division. ‘These may serve to some extent for the conveyance of mate- 
rial in the nutritive process, but seem principally to act as a kind of connective 
tissue through which the fibro-vascular bundles ramify, and outside of which the 
chlorophyll-bearing cells are borne. But in many plants, recorded by observers 
or examined by me, the nucleus in turn divides in a few of the cells at least. 
With such division there is no attempt at the formation of a cell plate, but 
the nuclear membrane either grows into the nuclear substance till separa- 
