2 
Elizabeth Acton. 
used to denote a certain section of the genus Cladophora, the 
members of which habitually form these conglomerate masses, and 
it is to this section that these balls belong. The specimens from 
L. Kildona have been identified as Cladophora (Aeg.) holsatica 
Kiitz. 
I. Structure of the Ball. 
The balls examined were collected from the surface of Lake 
Kildona at the end of August, 1907 and had been standing since that 
time in a dish in the laboratory with water dripping on to them. 
They were dark green in colour and quite hard and firm in texture; 
they varied from 2-3 cm. in diameter (Fig. 1, A). 
Fig. 1. Cladophora ( Aegagropila) holsatica Kiitz. A, whole ball; B, ball 
cut in half; C, mud removed shewing cavity of ball. All natural size. 1 
The balls when cut open show a central cavity filled with debris 
consisting of dead Aegagropila cells, fine mud and various minute 
algae in a more or less unhealthy condition. The outer shell is 
about 3 mm. thick and consists of a very tightly interwoven mass of 
algal filaments (Fig. 1, B, C). This tangled mass is made up of 
separate individuals which are tightly interlocked by special 
branches. Fig. 2, A, shows a small individual plant. 
Each plant shows a central axis of cells bearing tufts of 
branches (cf. Fig. 2, A). Any cell can produce branches and in any 
direction according to external conditions; so that the branch 
system tends to become irregular. Injury to the terminal cell has 
the effect of producing active lateral branching. 
A very noticeable feature of the cell is the extreme thickness of 
the wall, which is conspicuously lamellated and has knob-like projec¬ 
tions at the points where branches are about to form (cf. Fig. 3, D). 
The chloroplast is parietal and is made up of a large number of 
rounded plates. The cells of the vegetative branches are cylindrical 
and slightly swollen at the upper end but they tend to become 
irregular in shape as they get older (Figs. 2, 3). 
1 l am greatly indebted to Prof. G. S. West for this figure. 
