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POPULAR SCIENCE REVIEW. 
tions from the normal mode of growth are not uncommon. Frequently the 
prothalli form branches like themselves (secondary prothalli) which can 
again produce leaves and shoots in a great variety of forms. A moment’s 
reflection shows that the three ferns in question have lost the power of 
forming archegonia, and with it, sexual reproduction ; and as compensation 
for the loss of the sexual formation of the embryo, possess the power of 
forming the outgrowth described. This presents a special case of that 
general phenomenon which is called apogamy , total loss of reproductive 
power, and which consists in the fact that a species loses sexual reproduc- 
tion, and acquires in its place numerous non-sexual modes of propagation, 
such as brood-buds, suckers, &c. The numerous bulblets of the higher 
Phanerogams, species of Allium , Deutaria , and the like, are examples of 
this, as well as of the successive degrees of difference in apogamy.” — (Silli- 
mans Journal, May 1878.) 
CHEMISTRY. 
Two allotropic Modifications of Magnetic Oxide of Iron. — When iron ses- 
quioxide is heated for some hours to 850° — 440° C. in an atmosphere of hydro- 
gen or carbonic oxide, it is converted into the magnetic oxide. This substance 
is identical in properties with the product obtained either by calcining the 
hydrate of the magnetic oxide at 300° in a gas which is without action upon 
it, or by the decomposition of the carbonate of iron, or by tbe ignition of 
pyrophoric iron protoxide at a low red heat. It differs in a marked degree 
from that form of the magnetic oxide which we obtain on the employment 
of higher temperatures, whether by the decomposition of water by red hot 
iron, by burning iron in oxygen, or by the splitting up of the sesquioxide at 
a blight red heat. Magnetic oxide of iron, Fe 3 0 4 , is black and is strongly 
attracted by the magnet ; that variety, however, which is formed at lower 
temperatures by the processes referred to has a specific gravity of 4*80, is 
acted upon by concentrated nitric acid, and can undergo further oxidation, 
being changed by rusting into sesquioxide. The magnetic oxide formed at 
the higher temperatures is not changed into sesquioxide when heated in the 
air, is not attacked by strong nitric acid, and has a specific gravity of 5-0 — 
o'00. This is the variety which forms the little granules and spherules 
found in meteoric dust. Moissan, who has made these observations (“ Compt. 
rend.” 1878, lxxxvi. (500) determined some time since the existence of two 
allotropic modifications of iron protoxide : a pyrophoric modification 
obtained at temperatures between 350° and 450°, and a second and non-pyro- 
phoric variety produced, as Debray has shown, at temperatures between 1000° 
and 1200°. The first variety when oxidized is converted into sesquioxide, 
the second forms magnetic oxide only, and of the kind which is produced at 
high temperatures. If pyrophoric iron protoxide, which would be converted 
into sesquioxide by exposure to the air, be heated to a low red heat in a 
current of carbonic acid, it is oxidized to magnetic oxide, carbonic oxide 
being formed ; the variety of the magnetic oxide obtained by this operation 
is identical in character with that obtained at low temperatures. If magnetic 
