606 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
fixed in the same way to the apex of the mother-cell in an arborescent 
manner. The three genera Sciadium , Characium , and Baphidium are, 
therefore, nearly related to one another, and differ essentially from 
Pleurococcus in the absence of a true septation. 
Re-establishment of the Size of Diatoms.* — Dr. P. Miquel proposes 
to abolish the terms sporangial frustule and auxospore, as used in the 
description of diatoms ; and to apply the term “ mother-valve ” to the 
valve which a diatom retains during the whole of its existence, “ daughter- 
valve ” to that which a portion of the protoplasm carries with it in the 
formation of a new individual. The author gives the following account 
of the re-establishment of the original size and the restoration of the 
form, derived from the observation, under cultivation, of a vast number 
of individuals belonging to a variety of species of the genera Melosira, 
Cyclotella , Biddulphia , NitzscMa, and Navicula, 
The protoplasm contained in the microfrustule clothes itself with a 
thick extensible membrane capable of resisting the strongest mineral 
acids ; it appears to be composed of cellulose and hydrate of silica, and 
is formed before the protoplasm frees itself from the valves which 
imprison it in the microfrustule. The valves then separate, and are 
thrown off by the protoplasm ; the membrane which encloses the new 
cell is soft and flexible. The growth of the protoplasm takes place 
mainly, though not entirely, at right angles to the axis which joins the 
future nuclei, and continues until it has regained the size which it had 
lost by reduplication. As soon as it has attained this size, its external 
membrane secretes a siliceous envelope, which, however, is absent from 
the plane perpendicular to the axis of the nuclei. It is in this plane 
that the protoplasm divides to form two interior valves, the two first 
daughter-valves ; and these two halves of the original megafrustule 
produce, by reduplication, new generations of diatoms to the number 
of 2 n . 
The nucleus is the main agent in the regeneration of the size of 
diatoms. After the contents of the microfrustule have condensed and 
surrounded themselves with a firm membrane, this “ spore ” germinates, 
and produces an individual which is the diatom with its original size 
restored, and presenting, on its siliceous walls, the markings character- 
istic of the species. 
Without denying the possibility of its occurrence, the author has 
never observed, in any diatom, a process analogous to conjugation ; nor 
the breaking up of the contents of the siliceous frustules into a number 
of microspores. 
Movements of Diatoms. — Replying to the observations of Muller on 
this subject, Herr R. Lauterborn f repeats his statement that the frustules 
of Pinnularia major , nobilis , and viridis are surrounded by a distinct 
mucilaginous envelope, though this has not yet been detected in other 
genera, nor in P. oblonga. The strings of protoplasm projecting through 
the raphe, to which Muller ascribes the power of movement, are, 
* Ann. de Micrographie, v. (1893) pp. 521-47 (8 figs.); Le Diatomiste, ii. (1894) 
pp. 61-71, 88-98 (8 figs.). 
f Her. Deutsch. Bot. Gesell., xii. (1894) pp. 73-8 (1 fig.). Cf. this Journal, ante , 
p. 382. 
