464 
Palaeontologie. — Microscopie. — Algae. 
apically retained megaspore. On the other hand there is the possi- 
bility of its being a gland — somewhat on the lines of the familiär 
glands of Lyginodendron oldhamium. F. W. Oliyer. 
Spitta, G. J., Microscopy. The Construction, theory and use of 
the microscope. (John Murray, London 1907. 468 pp. 16 plates. 
215 figs. in text. Price 12 s. 6 d. net.) 
The author deals in great detail with the properties of lenses 
and the optics of simple and compound microscopes and their acces- 
sories. As examples of the very numerous subjects dealt with may 
be mentioned, a discussion of the differences between semi-apochro- 
matic and apochromatic objectives, including an account of spherical 
and chromatic aberration, — the evaluation of objectives and ocu- 
lars, — methods of illumination, — theories of microscopie vision, 
etc. The last chapter consists of practical hints upon the correction 
of a number of common “faults” met with in using the microscope 
and its accessories. Agnes Robertson. 
Davis, B. M., Spore Formation in Derbesia . (Ann. Bot. XXII. 
p. 1-9. pl. 1-2. 1908.) 
The author has investigated in cytological detail the develop¬ 
ment of the peculiar, multiciliate zoospores of Derbesia. Bert hold 
in 1881 had stated that the large single nuclei of the spores were 
produced by the successive fusions of very numerous nuclei within 
the sporangium. The author shows that several thousand nuclei 
pass into the sporangium; a certain number of them increase in size 
and become the future nuclei of the zoospores while the rest dege- 
rate without any process of fusion. The larger nuclei become con- 
spieuous by the development of numerous cytoplasmic Strands which 
radiate out from the cytoplasm enveloping the nucleus. The Strands 
have deeply staining granulös where they join the enveloping cyto¬ 
plasm just outside the nuclear membrane. When the larger nuclei 
have become distributed uniformly in the sporangium and the pro¬ 
cess of nuclear degeneration is practically ended Segmentation of 
the protoplasm begins. Cleavage Starts at the periphery of the pro¬ 
toplast and by curved and branching furrows the protoplasm is cut 
up into uninucleate masses. The nucleus of the spore then moves 
from the centre towards the periphery and about a third or fourth 
of the protoplasma Strands on the peripheral side of the nucleus 
become arranged in the form of a funnel. Granules are found on 
these Strands and these accumulate in a circle just underneath the 
plasma membrane and fuse to form a deeply staining ring, the ble- 
pharoplast. The nucleus passes back to the centre of the cell end 
and the blepharoplast splits to form two rings, from the lower of 
which the circle of cilia is developed. The two rings of the blepha¬ 
roplast remain for some time visible even in the germinating spore 
but they ultimately, no doubt, disappear. The relation of centrosome 
and blepharoplast is discussed and reference is made to the cilia 
forming apparatus in animals. The author points out that in Derbe¬ 
sia the nucleus has very intimate relation s to the development of 
the blepharoplast and that the latter does not arise from the plasma 
membrane, but from granules — which are not centrosomes — as- 
sociated with the protoplasm investing the nucleus. The author con- 
cludes that the peculiarities of the zoospore of Derbesia are later 
