io Structure and Origin of “ Cladophora Balls." 
According to Wesenberg-Lund (loc. cit.) the formation of the 
balls is primarily due to the incessant destruction of the terminal 
branches directed towards the exterior which causes the growth of 
new adventitious filaments. Where no external factor hinders the 
growth of terminal filaments the thallus is tufted with free branches. 
But the motion of the waves against a sandy floor supplies this 
factor and the harder the floor the more regular will be the shape 
of the ball. The greater irregularity of the balls of Aeg. Sauteri 
described by Lorenz (loc. cit.) from the Zeller See, and the absence 
of irregular forms from Lac Soro is due to the difference in the 
substratum in the two cases. In the Zeller See the floor is a soft 
lime and that of Lac Soro is sandy. 
According to Lorenz, light plays an important part in the 
formation of the balls. The more intense light in shallow water 
produces a more active growth and the motion of the waves exposes 
all parts to the light in turn and induces a radiating structure. He 
also thinks that a soft bottom favours the formation of the balls 
since it offers less resistance to the rolling of the balls. This 
explanation does not account for the death of the terminal cells 
which is a very noticeable feature in the branches directed towards 
the exterior. 
Wesenberg-Lund thinks that light isquite'a secondary factor. 
Brand (1906), 1 on the contrary, thinks that light is the chief factor, 
but operating in an exactly opposite way to that described by Lorenz 
He thinks that the death of the terminal cells and consequent 
increased formation of lateral branches is brought about by their 
successive exposure to light and not, as Wesenberg-Lund supposes, 
by friction against the sandy floor. The cells are too elastic and 
thick-walled to be injured to any great extent in this way. He 
shows that in balls exposed to a strong light in tanks, the outer 
part of the ball died and the branches started to grow towards the 
centre the inner part of the ball being a bright green. 
It is obvious, however, that whatever external conditions are 
are necessary for the formation of the balls, the peculiar character 
of the alga itself must play a very important part, for the balls of 
Aeg. holsatica which had been living for eight years in a small dish, 
exposed to unnatural conditions, still kept their spherical shape. 
In conclusion, I wish to express my thanks to Prof. G. S. West 
for suggesting this work and for advice during the investigation. 
The Botanical Laboratory, 
The University, Birmingham. 
1 F. Brand. “ Uber Cladophora crispata und die Sektion Aegagropila 
Hedwigia, Bd. 45, 1906. 
