382 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
but stages of development of the same form. Neither the presence or 
absence, nor the arrangement, of the spines can be relied on as specific 
distinctions. On escaping from the mother-cell Scenedesmus consists of 
four daughter-cells arranged alternately at different levels, which are set 
at liberty by the irregular splitting of the membrane of the mother-cell. 
The nearest alliance of Scenedesmus appears to be with Pediastrum. 
Prof. R. Chodat and Mdme. 0. Malinesco* * * § state that Scenedesmus is 
exceedingly polymorphic under cultivation. From a Pleurococcus form 
resembling Glceocystis Naegeliana they obtained, in distilled water, a 
form identical with Paphidium minutum. In an alkaline nutrient 
solution states were produced indistinguishable from Dactylococcus 
infusionum and Scenedesmus acutus. Scenedesmus has therefore a 
Protococcus , a Baphidium, and a Dactylococcus form. 
New Pleurococcus. j — Under the name Pleurococcus nimbatus Herr 
E. de Wildeman describes a remarkable new species, in which the single 
cells or colonies of cells are surrounded by an aureole of a radial-fibrillar 
structure, invisible in water, but very visible in a solution of Indian ink. 
Intra-frustular Reproduction of Diatoms.J — Dr. G. B. de Toni 
confirms the observation of Castracane of the formation of new frustules 
within the old ones in the case of Amphora ovalis. The young frustules 
agree altogether with the description of the alleged species A. minutissima. 
Movements of Diatoms. § — Herr O. Muller repeats his former 
explanation of the movements of diatoms as depending on forces con- 
nected with protoplasmic currents on the surface, and criticizes the 
conclusions which Biitschli has drawn from his own observations.!] The 
threads which this authority describes as proceeding from the central 
node are, according to Muller, composed not of mucilage, but of proto- 
plasm ; they do not project through the mouth of the canal, but are 
entirely external. He asserts that there is no gelatinous envelope, as 
described by Biitschli and Lauterborn ; that which has this appearance 
is the result of the treatment to which the diatoms have been subjected. 
A close examination of the phenomena negatives the hypothesis that the 
movement of the diatom is the result of the springing back of the thread ; 
it is rather due to currents of cytoplasm passing in and out of the canal 
and along the surface. 
Relationship between the Morphology and Biology of Diatoms 
and their Classification.! — Herr F. Schiitt reviews the various systems 
which have been proposed for the classification of diatoms. Those 
of Pfitzer and H. L. Smith are to a certain extent in harmony, the 
Placochromaticae of the former corresponding in the main to the 
Raphideae of the latter, the Coccochromatk ae to the Cryptoraphideae 
(or Araphideae). The author proposes to divide the Diatomaceae into 
two primary divisions, the ground-forms or those attached to a sub- 
stratum, and the plancton or floating forms; the latter are mostly 
Araphideae, the former Raphideae. Among the ground-forms two types 
* Bull. Herb. Boissier, i. (1893) pp. 184-90 (1 pi.). See Bot. Centralbl., lvii. 
( 1894) p. 69. f Tom. cit., p. 337. See Bot. Centralbl., lvi. (1893) p. 78. 
% Ber. Deutsch. Bot. Gesell., xi. (1S93) Gen.-Versamml.-Heft, pp. 74-5. 
§ Tom. cit., pp. 571-0 (1 fig.). Cf. this Journal, 1889, p. 793. 
I, Cf. this Journal, 1893, p. 769. 
! Ber. Deuisch. Bot. Gesell., xi. (1893) pp. 563-71 (1 pi.). 
