Problems in Aquatic Biology. 
169 
October and was hence only observed in 1904 (cf. my observations 
on the water-lily pond at Kew 1 ). It is thus commonest at the time 
of the second sexual phase of the pond, if I may he permitted to 
call it so. Coleocliactc scutata , growing on the leaves of Myriophylluvi, 
is present all the year round like this latter plant; it however attains 
its maximum development in the first half of the year, becoming 
sexual in the early part of the summer, i.e. during the first sexual 
phase of the pond. 
I hope the preceding pages will suffice to show the multitude of 
problems in the field of algal biology and ecology and will encourage 
their study. Many of the points indicated here will be dealt with 
in greater detail in the subsequent paper and will be supported by 
actual data obtained from numerous periodic and casual observations. 
Although much has been said in support of periodic investigation in 
this paper I do not wish to deny in any way the great value of 
casual observations, if they are undertaken with sufficient precision. 
In the elementary condition of our knowledge on these subjects 
every careful observation is of much value. I have omitted all 
mention of the analogous problems presented by sub-aerial algal 
growth; they are however best studied primarily in the Tropics 
where sub-aerial Algae play a far more important part than they do 
with us. A considerable contribution towards this subject is 
contained in the first part of my paper on the Algae of Ceylon, 
which will appear shortly. 
1 Fritsch, Annals of Bot. Vol. XVII. 1903, p. 276. 
DESCRIPTION OF CHART ON p. 160. 
Graphic representation of relative frequency and time of sexual repro¬ 
duction of the more important Algae in a pond at Telscombe near Newhaven. 
- = Oedogonium crispulum ; — = Spirogyra iusignis ;-= Oedogonixim 
inversum ;.- Spirogyra condcnsata ;-- Colcochaete scutata ; 
-- - Oscillaria tenuis ; —--— - Spirogyra gracilis ; 
_j—| —(—1 —(- indicates sexual reproduction, a = abundant; vc = very common ; 
c = common ; rc = rather common ; rr = rather rare ; r = rare ; vr = very 
rare. (N.B.—No samples were taken during August—December, 1903, so that 
the curves included in this part of the chart are hypothetical). 
