468 Carter . — The Cytology of the Cladophoraceae. 
outline, whilst Gay (1891) also figures coarsely reticulated chloroplasts in 
CL fr acta and Rhizoclonium hieroglyphicum . 
Kjellmann (1897) gives an account of the chloroplast ot Aegagropila 
canescens , which he says consists of a cylindrical parietal sheath, from which 
arises a network penetrating into the interior of the cell and consisting of 
very thin, almost colourless lamellae bound up in a cell-like mass. Kjellmann 
gives figures to illustrate this internal network, and it seems to be rather 
different from the coarse network described by Schmitz (1882), neither has 
any structure comparable with it been observed during the present work. 
Brand (1899, 1901, 1906 a) remarks on the form of the chloroplast 
in Cladophora. In the first paper he discusses the occurrence of chloroplasts 
in the form of spiral bands as described by Kiitzing (1843) for the summer 
condition of Cl. fracta , and Roth (1797— 1806) for Cl. crispata , and since he 
himself had never observed such chlorophyll bands, comes to the con- 
clusion that this appearance was not normal. In the second paper he 
remarks that in all the freshwater species of Cladophora he had examined, 
the characters of the chloroplast were similar to those described by Schmitz 
(1879, 1882), Strassburger (1880), and Kjellmann (1897), with the exception 
of the internal network, which could only be demonstrated in certain cases. 
Brand never observed a nearly uninterrupted parietal sheath such as was 
figured by Strassburger (1880), and is also of the opinion that the very thin 
drawn-out networks, and also the completely free small plates described by 
earlier investigators, are only found in extraordinary circumstances ; the 
former condition being general in cells which have become abnormally 
lengthened by long exposure to strong light, and the latter in cells turned 
away from the light and about to form rhizoids. In the last-mentioned 
paper Brand again comments on the so-called spiral chloroplasts of 
Cl. crispata . 
The genus Rhizoclonium has been investigated by Wille (1901), who 
finds that a peculiar feature of Rh. riparium is the presence of numerous 
short outgrowths proceeding from the external surface of the chloroplast 
towards the cell-wall. In Rh. Kerneri these outgrowths were much smaller, 
and in neither species could they be distinguished in the fixed and stained 
condition. Wille seems to think that these outgrowths of the chloroplast 
are obliterated during the process of fixation. 
With regard to the number of nuclei, it has generally been believed 
that the segments of Cladophora and Chaetomorpha contain very numerous 
nuclei, whereas in Rhizoclonium they are very reduced in number. Thus 
Borzi (1883) found that in Rh. hieroglyphicum the shortest cells contained 
only one nucleus, whilst in the longer segments there were sometimes as 
many as four, and Gay (1891) in one instance found five. Wille (1901) 
never observed more than four nuclei in either Rh . riparium or Rh. 
Kerneri. 
