164 
THE JOURNAL OF BOTANY 
reversed, namely between the ribs, the tissue is still visible, and the 
pericycle tends to be vacuolate. 
Apart from the somewhat unusual leaf-shape, A. drupaceus shows 
considerable superficial resemblance to the members of the sub-family 
Thunbergias of the Acanthacece. Certain leaf characters, such as 
absence of cystoliths and presence of typical somata are also charac¬ 
teristic of this sub-family. The andrcecium and fruit differ markedly 
from any known genus, but the remaining characters show affinity 
with Mendoncia, Afromendoncia, and Thunbergia. 
minute anatomy of the stem is almost exactly that 
Gilg in Ber. der Deutsch. Botan. Ges. 1893, p. 351, 
doncia. Reference may also be made to the account by lioulet of the 
anatomy of Thunbergia in Bull. Herb. Boiss. 1894, p. 259. 
Finally, the 
described by 
for Afromeii- 
FRESHWATER PLANKTON ALG/E FROM CEYLON. 
By W. B. Crow, M.Sc., Ph.D. 
(Concluded from p. 145.) 
Hydrodictyaceae. 
Pediastrum. 
Judging by the collections examined, P. simplex and P. duplex 
are the most important members of the Chlorophgeece in the plankton 
of Ceylon. They are frequently very abundant and, although not 
occurring in such vast quantities as the species of Microcystis , have 
a much wider range, occurring in habitats of very diverse type and 
occasionally the only phytoplankton present. The two species often 
occur together. It is noteworthy that only these two forms were 
observed in appreciable quantity, and many of the best-defined 
species in Europe were not met with. 
P. simplex Meyen. This shows very considerable variation in (<7) 
size of colony, ( b ) number of cells, and ( c ) shape and size of lacunae : 
these characters should therefore not be used as primary specific 
distinctions. The great amount of material often rendered the 
variation very striking, but no essentially new forms were met with. 
Apparently there is no direct connection between structure and 
habitat; very many collections, probably all in which the alga was 
present in sufficient quantity, show variation from the type to P. 
clathratum. The localities where this was the dominant type are 
recorded below. Probably several other microspecies or forms have 
been included here as also in the records of P. duplex ; but owing 
to the variability of the material it has not been practicable to 
separate them. Toe. 7, 10, 18, 19, 23, 26 (very abundant), 38, 39, 
41, 42, 45 (very abundant), 49, 50, 57. Distr. Cosmopolitan. 
P. clathratum (Schroeter) Lemm. Loc. 2, 13, 14, 26, 45, 53. 
Distr. Cosmopolitan (inch Ceylon). 
P. duplex Meyen (inch var. clathratum A. Br.). The material 
is so abundant and variable that it has not been possible to distin- 
