ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
661 
the systematic position of the host-plant, and several new species are 
described. The illustrations represent the characters of the genera. 
Myxomycetes. 
Ceratification in Myxomycetes and Myxobacteria.* — Herr H. 
Zukal describes a resting condition in certain Myxomycetes dependent 
on the conversion of the cell-walls of the plasmodes and receptacles 
into a horny substance. It was observed in Trichia fallax , T. varia , 
and Lycogala epidendron. In the first-named species the sporanges were 
in one spot converted into a reddish-brown mass of a horny consistence, 
the spaces between the spores, sporanges, and capillitium-filaments, being 
filled by a hard homogeneous transparent substance, in the place of air 
or a fluid protoplasmic mass. The process he believes to be a perfectly 
normal one, similar to the formation of sclerotes in Fungi, and enabling 
the plant to remain for a time in a state of rest. A similar phenomenon 
was observed in the other Myxomycetes named, also in two Myxobacteria, 
Chondromyces crocatus and Myxococcus macrosporus. 
Protophyta. 
a. Schizopliyceae. 
Reproduction of Diatoms.f — Count Abbe F. Castracane reviews his 
previous conclusions on the subject, and points out that the diminu- 
tion in size of diatoms by scissiparition takes place only in those genera 
where the two valves of the frustu’es are joined in such a way that one 
encloses the other ; in the Melosireae this diminution is compensated 
by the natural increase in size of the individual. He further notes that 
in Melosim various the frustules, usually described as cylindrical, are 
occasionally spherical. 
Decrease and Increase in the Size of Diatoms.^— Hr. P. Miquel 
has carried on for nearly three years a series of experiments on the 
decrease in size of Nitzschia linearis. He finds that, in 71 cultures, 
during this period, the greatest length is reduced from 70*2 to 39*0 /a, 
the average length from 63*6 to 33*6 /a. He calculates that the number 
of multiplications required for this reduction would be at least 1640, 
and that the number of individuals produced in these multiplications, 
represented by the expression 2 1640 , would exceed in mass that of our 
globe as much as a cubic metre exceeds a grain of sand, and could only 
be expressed by a series of mere than 500 figures. When the minimum 
size has thus been attained, a sterile microfrustule is produced, from 
which the author was unable to obtain auxospores. With Nitzschia 
sigmoidea, on the other hand, during a culture wdiich extended over 
several months, the amount of reduction was only from 170 to 130 /a, 
and microfrustules were then obtained which germinated, and re-estab- 
lished the original size. Similar results w r ere obtained with Nitzschia 
palea, N. elliptica, Cyclotella comta, Biddulphia aurita, B. rhombus , and 
Navicula elliptica. Abnormal auxospores and megafrustules were some- 
times produced, interrupting the regular course of diminution in size. 
* Biol. Centralbl., xviii. (1898) pp. 573-8. 
f Ann. de Micrographie, x. (1898) pp. 67-80. 
% Tom. cit., pp. 49-59, 182-91 (2 figs.). 
