312 Carter, — Studies on the Chloroplasts of Desmids. IV. 
the new semi- cells are formed there is no need for any change. In such 
forms it is rather the chromatophores which migrate. 
Cell-division was very similar in all the Placodermae investigated. 
The individual about to divide is usually very densely green, its chloro- 
plasts are coarsely granular, and neither their definite structure nor the 
position of the pyrenoids can be distinguished. The reason for this is 
doubtless that the chloroplasts are very distended with stroma starch, which 
gives them the shapeless granular appearance, and by its great refractivity 
obscures the pyrenoids. The cytoplasm is sometimes crowded with 
numerous colourless oily-looking globules. 
The division of the nucleus, accompanied by the elongation of the 
isthmus, and the subsequent formation of the transverse cell-wall are all 
completed before any visible changes take place in the chromatophores. 
The young semi-cells, still colourless, begin to round themselves off, and may 
even separate before anything further happens as far as the chromatophores 
are concerned. At this stage the protoplasm in the young semi-cells is 
becoming rather vacuolate, and its rapid streaming movements are clearly 
visible. Very often the daughter nuclei can be seen with high magnification 
as glistening bodies embedded in the protoplasm in the isthmus of each 
individual, and the colourless oily-looking globules may stream into the 
young semi-cells from the old one (Fig. 61), When the young semi-cells 
have attained a fair size, the chloroplast in each of the older half-cells begins 
to protrude slightly through the isthmus on each side (Fig. 62). This small 
part budded into the isthmus continues to increase in size as more and more 
of the chloroplast streams in from the old semi-cell into the rapidly growing 
young one. As the young semi-cell is gradually filled, the chloroplast con- 
tracts visibly from the wall of the older one (Figs. 62-5). Once the process 
has begun it continues very rapidly for a time ; thus the period of time 
between the stages represented in Figs. 62 and 64 is only half an hour, and 
at the end of another half-hour the young semi-cells have begun to assume 
their characteristic form, and contain nearly as much of the chloroplast as 
the old ones (Fig. 65). The subsequent growth of the individuals was not 
so rapid, but in less than six hours after the beginning of the process 
the chloroplast had not only completed its budding, but in both old and 
young semi-cells had spread itself out so as to mantle completely the whole 
cell-wall, both individuals being now uniformly green (Fig. 67). 
It now only remained for the chloroplast to divide at the isthmus. As 
observed in living specimens under the microscope this final process was 
very slow, and in many cases, in spite of the use of various arrangements to 
ensure a free supply of water between the slide and cover-glass, the 
individual often died before the chloroplasts had completed their division. 
In the specimen of E nostrum Didelta figured, the division was complete 
except for the final breaking of the thin strand connecting the two halves of 
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