On Diatoms and a Parasitic Alga. 175 
VIIL—On the Relations between certain Diatoms and the 
Fisston-products of a Parasitic Alga (Chlorochytrium). 
By H. Cuartton Bastian, M.A., M.D., F.R.S., F.L.S8. 
[Plate XV.] 
Muc# interest was excited in 1872 owing to the discovery by 
F’. Cohn * of an alga existing as a parasite in the thallus of 
the ivy-leaf duckweed (Lemna trisulca). This was followed 
in 1877 by the discovery of another parasitic alga by Prof. 
Perceval Wright } infesting various marine alew. Since this 
time several other forms have been discovered, and rather an 
extensive literature has grown up concerning Chlorochytrium 
and allied genera. A key to some of this literature will be 
found in de Tonis’s ‘ Sylloge Algarum,’ vol. i. (1889) p. 636, 
in which an attempt was made to classify the various species 
then known. 
Among the new forms there is one, Ch. Knyanum, found in 
Lemna gibba and in L. minor, which was examined and 
figured by G. Klebs ft in 1881. This is evidently the alga 
that I have of late met with very abundantly in both these 
species of duckweed, and to which my present remarks will 
refer. 
I find during autumn and winter among duckweed from 
various localities many dead and decolorized leaves, having a 
greyish-white and somewhat gelatinous appearance. Such 
leaves may be easily picked out by spreading some of the 
duckweed in a thin stratum of water over a white dish. It 
will be found that the decolorized leaves are all devoid of 
rootlets, and possibly this loss of the rootlets may have been 
the main cause leading to the premature death and change 
in the appearance of the leaves. 
Examination with a hand-lens, magnifying eight or ten 
diameters, will show in many of such leaves that the upper 
greyish-white surface is flecked with minute specks of an 
emerald-green colour, sometimes abundantly and sometimes 
sparsely, while examination of these or other leaves under 
the microscope will often show an abundance of the early 
stages of such bright green specks, so minute as to have 
been invisible with the mere hand-lens. 
It is best to pick out the smaller leaves for microscopical 
* ¢ Beitrage zur Biologie der Pflanzen,’ Heft xi. p. 87, 
+ Trans. Roy. Irish Acad. vol. xxvi. p. 13. 
t Botan. Zeitung, 1881, p. 248, t. iii. figs. 11-165, 
