ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
455 
Plankton-Algae of the Freshwater Lakes of Norway.* — Under 
the name Elakatothrix gelatinosa g. et sp. n., Prof. N. Wille describes 
a new plankton-form from the lakes of Western Norway. The cells 
before division are fusiform, arranged originally in a row, and are sur- 
rounded by a gelatinous sheath. The cells divide only by transverse 
septa, and contain a small nucleus. The chromatophore, which occupies 
almost the entire cell with the exception of the ends, is parietal, and 
contains a large pyrenoid ; no swarm-cells were observed. Related to 
Adinastrum. Also a new species, Crucigenia irregularis. 
Fungi. 
Impregnation and Development of the Oosphere in Perono- 
sporeae.f — Prof. A. N. Berlese has turned his attention chiefly to 
Cystopus Portulacse , Peronospora Ficarise , P. effusa , P. Alsinearum, and 
P. parasitica. He was able to follow the act of impregnation, and the 
complete course of development of the oogone and oosperm, the follow- 
ing being the most noteworthy observations made on these and on 
other species. 
The Peronosporeas possess distinct sexual organs, the antherid 
and oogone ; and the act of impregnation does not consist in the osmotic 
mingling of their contents, but in the fusion of a male and female 
nucleus. The embryonal nucleus divides frequently until the oosperm 
is mature. In each daughter-nucleus the number of chromosomes is 
double that of the separate sexual nuclei. A reduction first takes place 
on the entrance of the oosperm into the germinating period, and the 
number of chromosomes is then reduced by one-half in the nuclei, and 
each of the daughter-nuclei becomes a zoospore. In several species 
the wall of the oogone remains permanently thin ; and then the peri- 
plasm becomes differentiated into a “ perinium ” (in Strasburger’s sense), 
with a more or less complicated structure. Even in those cases where 
they are well differentiated, the exospore and endospore cannot be re- 
garded as analogous to those organs in other fungi ; the exospore cor- 
responding rather to the “ perinium ” of certain Pteridophyta, and the 
so-called “ endospore ” to a true exospore. In other cases the wall of 
the oogone becomes thickened at the expense of the periplasm, and 
often forms a stout yellow or yellow-brown membrane. When there 
is no perinium, this wall serves as a protection to the oosperm during 
ripening and germination. 
Parasitic Fungi. — Herr von Derschau J describes the life-history of 
Exoascus deformans , and the changes produced in the flowers and tissues 
of the peach. 
Mr. B. M. Duggar § details the life-history, appearance, and remedies 
of the following diseases of the pear : — leaf-spot, due to Septoria pyricola ; 
leaf-blight, to Entomosporium maculatum ; and pear-scab, to Fusicladium 
pirinum ; also the bacterial disease pear-blight, due to Bacillus amyli- 
vorus. 
* Mittlieil. Biol. Geselh Christiania, Oct. 17, 1895. See Biol. Centralbl. xviii. 
(1838) pp. 802. 
t Jahrb. f. wiss. Bot. (Pfeffer u. Strasburger), xxxi. (1897) pp. 159-96 (4 pis.). 
X Landwirth. Jahrb., 1897, p. 897. See Bot. Centralbl., lxxiv. (1898) p. 112. 
§ Cornell Univ. Agric. Exp. Stat., Bot. Div., Bull. No. 145, 31 pp. and 15 figs. 
