ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
189 
perforations being in tlie external plate. Anotlier class of Triceratia, in- 
cluding T. majus , seem to consist of but one plate strengthened by cost® 
and pierced at rather wide intervals. 
Auliscus seems to consist of but a single plate with tubular perfora- 
tions ; as also do those species of Actinoptychus which do not show the 
coarser reticulations. Where the latter are present, they might be re- 
garded as analogous to the “ honeycomb ” layer of Goscinodiscus or Tri - 
ceratium, being evidently raised above the general surface. The inner 
plates, which can frequently be removed from valves of this genus, are 
not regarded as corresponding to the inner plates of areolated form, 
but merely as thin reproductions of the valve. 
Many species of Aulacodiscus resemble A. Sollittianus in structure ; 
but another class, such as A. Bogersii , have a radically different struc- 
ture, which, owing to their being very opaque when viewed on edge, 
Mr. Keeley has so far been unable to satisfaciorily elucidate. 
With regard to the film of silica presumed by some microscopists to 
exist over the entire surface of living diatoms, and destroyed by clean- 
ing, a careful study of living forms, action of stains, &c., has failed 
to show any evidence of its existence. 
Fungi. 
Penetration of Fungi into Calcareous Rocks and Bone?.* — Ac- 
cording to experiments made by Herr K. Lind, the penetration of fungi 
and bacteria into rocks is largely due to a chemical irritation. If a thin 
plate of chalk, marble, or bone is moistened on one side by a nutrient 
fluid, and the spores of fungi sown on the other side, the fungi will per- 
forate the plate ; while, if the spores are sown on the side moistened 
with the nutrient fluid, or if both sides are moistened, no perforation 
will take place. Many fungi also secrete considerable quantities of 
carbonic and oxalic acids, which have a powerful effect in corroding 
limestone. Of the three fungi chiefly experimented on, Botrytis cinerea 
displayed the greatest power of corrosion, next Penicillium glaucum, and 
lastly Aspergillus niger. The author points out the importance of these 
observations in practical dentistry. 
Effect of Aqueous Solutions on the Germination of Fungus 
Spores. t — As the result of a long series of experiments on different 
fungi, Mr. F. L. Stevens states that various fungi offer very different re- 
sistance to poisons, and that the limits of resistance vary in the same 
species. In general the results are in accord with the theory of hydro- 
lytic dissociation. Uromyces offers the greatest range in its susceptibility 
to poisons ; while Penicillium offers the greatest resistance. Peculiar 
knotted or twisted hyphee frequently result from the attempt to grow in 
a poisonous solution. 
Monograph of the Peronosporace8e.| — In the present instalment of 
his account of the Peronosporace®, Prof. A. N. Berlese gives a descrip- 
tion of the different modes of fertilisation that occur in the family. The 
sexual act does not consist in an osmotic diffusion, as suggested by de 
* Jahrb. f. wiss. Bot., xxxii. (189S) pp. 604-31 (3 figs.). 
t Bot. Gazette, xxvi. (1898) pp. 377-406 (1 fig.). 
J Riv. Patol. Veg., vii. (1898) pp. 19-37. Cf. this Journal, 1898, p. 657.' 
