NOTES AND MEMORANDA. 
257 
The stratum of sporophores was from xi^^^ yi^^^ 
thick The spores were the -g^^^rd mm. in diameter. 
By transmitted light the spores appeared so faintly coloured that 
the tint was undetermined ; by reflected light, in mass they appeared 
of a greenish hue. The receptacles including the sporophores ap- 
peared fuscous by transmitted light, but white by reflected light. 
In M. Eobins' plate of A. nigrescens he represents most of the 
fruiting stems as articulated, but in our plant none of this character 
were detected. 
NOTES AND MEMOEANDA. 
An American View of the Advantage of High Angular Aperture. 
— Mr. A. F. Dod, of Memphis, Tenn., U.S.A., has been inquiring into 
this subject, and has published the following very remarkable results 
in the ' American Naturalist,' * a journal which we had before very 
highly esteemed. Mr. Dod says : 
" Dr. Carpenter lays down as a fixed law the statement that * all 
who have made much use of the microscope are now agreed as to the 
superior value of objectives of moderate or even comparatively small 
angle of aperture for ordinary working purposes, the special utility of 
the very wide apertures being limited to particular classes of objects.' t 
" It is now claimed that this no longer holds good, and our inves- 
tigations were undertaken simply with a view to testing the correctness 
of this statement. 
" The glass we selected as the representative of the wide angles 
was a ' four-system ' immersion yV*^? ^f nearly 180° ; the narrow 
angles with which it was compared were the best at our command, by 
leading makers of England, Germany, France, and America, and com- 
prised both dry and wet systems. Bearing in mind the theory that 
the wide angles are only superior on diatoms and with oblique illumin- 
ation, we discarded diatom tests, and used only central light. 
" The first slide selected was a specimen of mosquito scales, dry. 
Under the ^^th of nearly 180° this object was beautifully defined, the 
structure of the intercostal spaces, longitudinal ribs, and terminal 
spines being all sharply and clearly shown. Even under so high eye- 
piecing as |th inch solid (equal to D), the object was splendidly 
illustrated. The narrow and moderate angles were then successively 
brought to bear on the same object, with the uniform result that, while 
not giving so good definition under low power eye-pieces, under the 
high eye-piece all utterly broke down. The next test selected was a 
slide of voluntary muscular fibre, in balsam. Here again the nearly 
180° glass gave splendid results, the definition of the striae being 
perfect, even under D eye-piece. The moderate angles were again 
brought on the field, with the same result as before. 
" These facts seem to justify the claim that the law, as laid down, 
touching the general usefulness of the wide-angled glasses, is not now 
* Apri], 1875. t Carpenter, 4th ed., p. 172. 
