64 
POPULAR SCIENCE NEWS. 
[May, 1891. 
The most striking peculiarity of tlvjs and other 
balanced stones is the -fact that they can readily 
be made to move, or oscillate, by the application 
of a comparatively weak force. The stone of 
Tandil, for instance, can be moved by pusliiug it 
with a single finger; but the center of gravity is 
so low that only a small amount of vibration can 
be produced, and it would not be possible to over- 
turn it by any ordinary means. 
The cause of the balancing of these rocks is not 
very mysterious. Nearly all boulders are more or 
less spherical or rounded in sliape, and if such a 
stone is deposited on a ledge of rock or other flat 
surface, it will naturally fall into a position of 
the greatest stability — that is, the center of grav- 
ity of the mass will take the lowest possible posi- 
tion. If this position is such that it brings a 
rounded surface of tlie stone next to the support- 
ing surface, the whole mass will be supported in 
stable equilibrium upon a comparatively small 
point, and an extremely small force will cause it 
to move upon that point. It is simply a case of 
natm-al balancing, due to the shape of the rock 
and the force of grav- 
itation. 
This principle can 
be well illustrated by 
taking a large double 
convex lens, — suclias 
a reading-glass, — and 
placing it upon a table 
or other flat surface. 
When left to itself it 
will always take one 
and the same posi- 
tion, and wliile the 
slightest force — even 
that of the breatli — 
will cause it to move 
upon its point of sup- 
port, it cannot be 
overturned until it is 
raised up to a per- 
pendicular position. 
Some years ago an en- 
terprising tourist suc- 
cessfully attempted 
the experiment of 
overturning one of 
these natural bal- 
anced rocks in Eng- 
land, but was very 
properly compelled 
by the indignant inhabitants of the neighborhood 
to replace it in its original position, at an expense 
far exceeding, we presume, tlie pleasure he derived 
from gratifying his curiosity. 
the class. They vary a good deal in size ; perhaps 
the most common pond species are six or eight 
inches in length. It is seen that the general parts 
of the plant are an axis, or central stem, and 
appendages borne at intervals along the stem. 
In early summer the only appendages are leaf- 
like parts arranged in whorls about the axis, but 
later branches grow out from the axils of the 
leaves, and in midsummer tlie orange-colored fruit 
appears. The plants are fixed to the muddy bot- 
toms by delicate processes which are not true 
roots, but rather root-hairs. 
The Characem are sometimes called stoneworts, 
from the fact that they have a hard, stony texture, 
due to the presence of a coating of carbonate of 
lime. To the touch they are liarsh and rough, 
like sandpaper. The central stem, it is observed, 
is made up of a series of jointed parts, exhibiting 
a structure that is termed serial homology, or 
repetition of like parts. The places at which the 
appendages are given oft" are the nodes, and the 
parts between the internodes. Each interuode 
consists of ii single large cell, wiiile a node is 
[Original in Popular Science News.] 
STUDIES IN PLANT BIOLOGY. 
BY PKOF. JAMES H. STOLLEK. 
III. 
A COMMON W^ATER PLANT. 
The plants that grow in water are naturally 
less well known than terrestrial ones, but some of 
our common aquatics are among the most inter- 
esting plants for biological study. For present 
examination we choose one of the class Characece, 
which are common fresh-water plants, growing 
submerged in ponds and streams, often covering 
the bottom with a thick green growtl>. The 
plants may be pulled up with the hand or dredged 
with a rake and placed in a jar of water, where 
they will live a long time. 
The accompanying figure shows the general 
appearance of any one of the numerous species of 
Fig. 1. 
made up of a group of relatively small cells. The 
plant grows in length by the constant addition of 
new nodes and internodes formed at the summit 
of the axis. It is seen fhat the internodes at the 
lower part of the axis are of about the same 
length, but towards the top they are gradually 
shorter, until at the end (as the microscope shows) 
many very short nodes and internodes are crowded 
together into a kind of bud. The terminal point 
of this bud consists of a single cell, called the 
apical cell, by the repeated divisions of which new 
nodes and internodes are constantly being formed. 
Thus the process of growth of the stem of a chara 
plaut may be represented as follows : Let it be 
the apical cell ; it divides, becoming two cells, a 
and 6, of which a is superior in position and is, in 
fact, a new apical cell. The inferior cell, 6, divides, 
giving rise to two cells, i and n. Of these, i, 
wliich is superior in position, increases in size but 
does not further divide; ra, on the other h;ind, 
divides several times, becoming a horizontal row 
of cells. The latter form a node, and i, which 
meanwhile has become an elongated cylindrical 
cell, forms an interuode. Thus a new node and 
internode has been derived from 6, and a remains 
to repeat the process. The leaves have essentially 
the same structure as the stem, consisting of a 
short row of alternating nodes aud internodes. 
The leaves are derived from the nodal cells of the 
stem by a process like that just described. The 
branches are exactly like the stem in structure. 
A single cell of chara, especiall}' an internodal 
or leaf cell, when placed under the microscope 
presents a most interesting spectacle. Tlie proto- 
plasm is arranged in two layers, an outer one, 
containing chlorophyll grains, and an inner layer 
of white granular protoplasm, called the primor- 
dial utricle. Now the latter is in a state of constant 
motion. Streaming up along one side of the cell, 
crossing at the end and moving downward along 
the opposite side, the movement goes on steadily 
hour after hour. In young cells the cell-nucleus 
can be seen carried along in tlie current ; in older 
cells the nucleus seems to have become disinte- 
grated, but the granules of the protoplasm render 
the current readily detectible. This phenomenon 
of the rotator}' move- 
ment of protoplasm 
within its cell-\Aall, 
is one, the cause of 
which has not been 
adequately deter- 
mined. It is proba- 
bly a process common 
to vegetal cells, being 
conspicuous in chara 
only because its cells 
are relatively very 
large. 
We may next notice 
what is spoken of as 
the fruit of the chara. 
This consists of small 
orange-colored bod- 
ies, about as large as 
the head of a pin, 
borne at the nodes. 
They are of two 
kinds, diftering in re- 
gard to the sexual 
nature of the cells 
developed in tliem. 
One, called tlie oogo- 
nium, contains wlien 
ripened a single germ- 
cell; the other, 
which is termed the antheridium, develops a 
very large uumber of minute bodies which are the 
male reproductive cell. An examination of these 
organs with the aid of the microscope is an inter- 
esting study. The oogonium is ovoid in shape, 
aud on the outside is made up of elongated aud 
spirally arranged cells. At the free end is a 
cliimney-like process, the hollow of which is filled 
with a soft mucilage. This mucilage is in contact 
with the germ-cell whicli lies within the case 
formed by the spirally-coiled cells. Thus the 
germ-cell is securely protected, .and at the same 
time is separated on one side from the external 
medium, the water of the pond or stream, only by 
the permeable mucilage. To understand the 
advantage of this arrangement we must first 
examine the other reproductive organ, the anthe- 
ridium. This is spherical in shape, and its 
exterior consists of eiglit cells which nicely dove- 
tail into each other, forming a complete case. 
Within are other cells which serve as points of 
attachment for very many loug-coiled filaments. 
In all, each antheridium contains from onei 
hundred to two Imndred of these filaments, and 
