66 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
found in the cytoplasm, where they can be observed during the condition 
of rest of the cell. The nucleoles are, as a rule, resorbed during the 
early stages of division of the nucleus, although in Psilotum they some- 
times persist till a later period, and were then mistaken by Karsten for 
nucleoles. The true centrosomes may be distinguished from nucleoles 
by several characters — by their size, which varies only within narrow 
limits, by the presence of a central corpuscle which stains more strongly 
than the surrounding zone, and by their constant position at the two 
poles of the nuclear spindle. Their average diameter is from 2 to 3 p, 
while that of the nucleoles varies between 2 and 5 /x. The process of 
nuclear division in the formation of the mother-cells of the spores of 
Psilotum are described in detail. The presence of nucleoles in the 
cytoplasm after the nucleus has lost its membrane and entered into the 
dividing stage, is not very uncommon. Herr Karsten confirms altogether 
the observations of Humphrey on this subject, and is unable to sub- 
stantiate those of Farmer. * 
(2) Other Cell-contents (including- Secretions). 
Starch-grains.t — Hr. A. Zimmermann gives a resume of recent 
literature on starch-grains. The newest observations are referred to 
on their mode of growth, their finer structure, and the mode in which 
they are absorbed. In connection with true starch, the literature is 
also referred to of the following allied substances : — Floridese-starcli 
(Rosanoff), Fucosan or PhaBophycese-starch (Schmitz), Fungus-starch, 
cellulin-grains (Pringsheim), fibrosin-bodies (Zopf), cellulose-grains 
(Weber van Bosse). 
Aleurone-grains.J — Dr. A. Zimmermann reviews recent researches 
•on aleurone- or protein-grains, with especial reference to the following- 
points : — their demonstration and permanent preservation ; their mode 
of formation and their connection with the vacuoles ; and the sub- 
stances contained within them. The allied substances are also referred 
to known as myrosin (Cruciferae and Tropseolum) and emulsin (Amyg- 
daleae). 
Protein-crystalloids.§ — We have from Dr. A. Zimmermann an 
account of what has been recently written on protein-crystalloids, with 
reference to their occurrence in Fungi, Algae, Pteridophytes, Gymno- 
sperms, Monocotyledons, and Dicotyledons. Their special reactions are 
then described, as are the researches on the question whether they are 
formed in the cytoplasm or the cell-sap. Reference is also made to 
the rhabdoids or plastoids observed by Gardiner in Bionsea , and to 
the spiny bodies ( Stachelkugeln ) of the Characeas. 
Existence in Plants of principles which are readily doubled, 
with production of carbon dioxide. (] — By a series of experiments 
(chiefly on leaves of the ivy and on the sugar-cane) MM. Berthelot and 
G. Andre have demonstrated the existence in vegetable tissues of sub- 
stances which set free carbon dioxide by a process of doubling going 
on within the tissues, without oxidation by the carbon dioxide of the air. 
* Cf. this Journal, 1894, pp. 581, 583. 
t Bot. Centralbl., 1894, Beili., pp. 329-35. X Tom. cit., pp. 321-4. 
§ Tom. cit., pp. 324-9. |) Comptes Rendus, cxix. (1894) pp. 711-4. 
