473 
Carter . — The Cytology of the Cladophoraceae . 
association with the pyrenoids that here also it is quite impossible to 
distinguish between definite colourless cytoplasm containing nuclei and 
chloroplast with pyrenoids (Figs, i and d). 
The structure is very suggestive of -that described by Timberlake (1901) 
for Hydrod ictyon . Timberlake found that in this alga the nuclei and pyre- 
noids often occurred in such intimate connexion that he was unable to 
distinguish a definite chromatophore, and so he decided that the chlorophyll 
must be diffuse and evenly distributed throughout the cytoplasm. The 
nuclei are nearly always in the same close association with the pyrenoids 
in the Cladophoraceae, but since it is sometimes possible to distinguish 
a coarsely reticulated chloroplast lying against the cell-wall with colourless 
interstices, it is quite obvious that in this case the chlorophyll cannot be 
diffuse. In these forms it is rather that the chloroplast has become so 
massive and has invaded the cytoplasm to such an extent that it naturally 
engulfs the nuclei as well. Moreover, the nuclei seem to prefer this position 
within the chloroplast rather than the colourless cytoplasm itself, for even 
in cells where the parietal film of chloroplast is very scanty, and more of 
the lining layer consists of colourless cytoplasm than is occupied by the 
chloroplast, the nuclei are still to be found in the chloroplast itself, although 
there is plenty of room for them in the colourless cytoplasm filling in the 
interstices (Fig. 3 ). 
Borgesen (1913), although not remarking particularly on the position of 
the nuclei, similarly figures these bodies apparently within the chromato- 
phores in two members of the Siphonocladiales, Cladophoropsis membranacea 1 
and Siphon ocladus tropicus . 2 • In another species, however, Boodlea Siam - 
ensis , 3 the nuclei are figured in the colourless cytoplasm lining the cell- 
wall, between the chloroplasts, whilst in Dictyosphaeria favulosaf Chamae- 
doris Peniculump and Ernodesmis verticillata 6 the nuclei are described as 
being either near to or underneath the chloroplasts in the cell-plasma. Thus 
it is quite possible that Borgesen really intended that in the first two species 
also, the nuclei should be imagined to lie in the protoplasm under the 
chromatophores, but this point is not made absolutely clear. 
There seems to be no doubt, however, that in the species of Cladophora 
and Chaetomorpha examined during this investigation most of the nuclei 
are immersed directly in the chloroplast. It is only very rarely that one 
meets with a nucleus in the interior of the cell which is not in close asso- 
ciation with pyrenoids, and might possibly be quite free from the chloro- 
plast. 
The same remarks apply with very slight modification to Rhizoclonium 
hieroglyphicum . In a very narrow form examined, the chloroplast was con- 
fined almost entirely to the peripheral parts of the cell, forming a very thin, 
1 p. 47- 2 P- 66. 3 p. 50. 4 p. 34. 
5 p. 58. 6 p. 68. 
