146 
POPULAE SCIEI^CE NEWS. 
[October, 1891. 
The current-breaker may also be used to good 
advantage as an automatic fire alarm, by making 
the hook to which the bulb is hung of fusible 
metal, or even tying it with a piece of light cotton 
thread. When the temperature rises sufficiently 
to melt the fusible metal, or if a flame occurs so 
as to burn the thread, the bulb will fall down, 
breaking the circuit and sounding an electric bell 
or other alarm. 
As shown in the engraving, the apparatus is 
designed to be used on a closed circuit, that is, 
one where the current is continually passing. If 
used on an open circuit it is only necessary to seal 
the wires into the opposite end of the bulb, so 
that when it is released from the hook the mer- 
cury will surround the wires, thus completing the 
circuit. 
•♦♦ 
[Original in POPULAK SCIENCE NEWS.] 
THE DEVELOPMENT OF DEVICES FOR 
CROSS-FEKTILIZATION IN PLANTS. 
BY C. SIGMUND KATJE. 
Flowers naturally fertilize themselves, being, 
as a rule, provided with organs of both sexes. 
The stamens produce the male element (pollen), 
and the style should normally ripen its stigmatic 
surface at the time the pollen is ripe, so that it 
may receive the latter, and the ovules be ferti- 
lized. The manner in which this takes place is as 
follows : 
Pollen consists of minute grains, each being 
provided with an external coat called the extine, 
and an internal called the entine. The shape of 
the pollen varies, depending mainly on the way 
in which it is to be conveyed to the stigma of 
another flower. For example, that to be con- 
veyed by insects Is generally rough or viscid; 
that to be carried by the wind is, on the other 
hand, smooth and dry. We thus see that the 
character of the pollen is already a step to aid 
cross-fertilization. Now when a ppUen grain 
lands on a mature stigma, it begins to at)sorb 
moisture from the latter. Consequently the eon- 
tents begin to swell, and the inner coat protrudes 
through the extine as a blind tube, therefore 
called a pollen tube. This pollen tube forces Its 
way through the style into the ovary, when it 
finally enters an ovule and fertilizes it. It is thus 
evident that two conditions are necessary for fer- 
tilization, namely : that the pollen be ripe, and 
that the stigma be prepared to receive it. 
The simplest device a perfect flower could there- 
fore offer to promote cross-pollenation would be 
to ripen its parts at different times. Flowers 
doing this are designated as being dichogamous ; 
if the pistil ripens first they are called proterogy- 
nous, while if the stamens ripen first they are pro- 
terandrous. Next we see special arrangements of 
the parts, deviations in length, and other minor 
points. Take, for example, the cowslip {Prirmila), 
which has two forms, named, respectively, the 
long-styled and the short-styled forms, by Dar- 
win. In the short-styled form the stamens — 
which are situated on the throat of the corolla — 
are high up, right at the mouth of the tube, and 
the style is short, reaching about half-way up. 
In the other form the style is long, and reaches to 
the mouth of the corolla, while the stamens are 
seated about half-way down the tube. It can 
easily be seen that an insect visiting the first 
named form (short-styled) would get thoroughly 
dusted with pollen, and on a visit to a long- 
styled form would first of all rub against the pro- 
truding style and deposit the pollen. Darwin 
was the first to explain the sigultlcance of this 
arrangement. 
In the Compositm the anthers of the stamens are 
united into a tube surrounding the style. The 
pollen ripens early, and, as the anthers open in- 
wardly, it remains in the tube after being de- 
hisced. The style keeps on growing and forces 
the pollen out of the tube, generally aided by a 
crown of hairs, its action being similar to that of 
a ramrod. Thus the pollen is scattered over the 
top of the flower, and the style having attained 
its gi-eatest length spreads out its two branches, 
displaying the ripe stigmatic surfaces. These 
flowers are proterandrous, and an insect visiting a 
head will easily scatter the pollen among the 
stigmas. 
We will next examine a bunch of flowers from 
the Indian-bean tree (Catalpa bignonioides) , and 
note the manner in which it has developed a 
means for cross-fertilization. The flower is some- 
what two-lipped, with five irregular lobes to the 
corolla, and a groove in the under lip leading into 
the tube. The stamens are two, and open — as it 
would seem — inwardly, but they really open out- 
wards (extrorse), because the pistil is in back of 
them. In a young flower the style is pressed 
against the upper lip of the corolla by the two 
stamens, which, as has already been stated, shed 
their pollen from the pistil, and so cannot possibly 
fertilize it. We may call this the first stage (Fig. 
1). Later, when the pollen has been shed, the 
stamens relax, and the style forces its way 
through them and bends downwardly into the 
tube of the corolla, at the same time ripening the 
two stigmatic surfaces which spread apart. ITiis 
may be called the second stage (Fig. 2) . It can 
r. 
7'- 
^/•^- 
now be seen that an insect on entering a flower in 
the first stage would get its back dusted with pol- 
len, and on coming in contact with the ripe and 
declining style of a riper flower, it would invari- 
ably fertilize the same. Has this arrangement 
always existed in the Catalpaf There are a few 
l)oints which might prove that this is not the 
original state of the flower, and that fonnerly it 
was regular and fertilized itself. The tliree stam- 
inoidea at tlie base of the corolla account for the 
three missing stamens, and the reason they have 
atrophied is, there was no use for them. The tor- 
sion in the filaments of the two remaining sta- 
mens, wliich can plainly be seen, has taken place 
from within outwards, comprising a turn of 180°. 
Without these changes we would have a flower 
with five stamens oijening toward the pistil, mak- 
ing it possible to fertilize itself. 
So we see that the necessity for cross-fertiliza- 
tion among plants is so great that they will de- 
velop for themselves devices which almost seem 
to be the result of a reasoning process. 
Among the recent importations at San Francisco 
are large quantities of sulphur from Japan of re- 
markably pure grade. 
[Original in Popular Science News.] 
AN HOUR IN THE BOTANICAL GARDENS 
OF PADUA. 
BY ADA M. TROTTER. 
Padua, a small town of 47,300 inhabitants, 
bears the honor of possessing the oldest botanical 
gardens in Europe, founded by the republic of 
Venice in the year 1545, at the suggestion of the 
learned Professor Bonafede. The change from 
the intense glare of the stone paved streets to the 
shade of these beautiful gardens was to be appre- 
ciated, perhaps, only by those who had wandered 
from one to another of the tortuous ancient ways 
of Padua in this fierce July sun. It was indeed a 
transition from hades to paradise. 
The first thing which attracted my attention 
was a fine plant of Acanthus mollis in full flower, 
each white blossom overlaid with a leaf of inex- 
pressibly delicate purple tint. I had seen the 
plant in April, growing freely in the temples at 
Pajstum, (Southern Italy), but hitherto had 
never seen the blossom. The Acanthus longifolius 
also flourished here, but was not in blossom. 
Close to the Acanthus is a very beautiful specimen 
of Negundo fraxinifolium, (_Albo virens), making all 
others which I had formerly seen shrink into 
nothingness in comparison. But the Tulipifera 
from the United States, near by, though sixty 
feet high, has many a rival among the mountains 
of North Carolina. 
Some of the trees in the gardens of Padua have 
a world-wide renown ; for instance, the Platanus 
orientalis, from Asia Minor, planted in the year 
1680. Though the trunk is hollow, the tree flour- 
ishes, and covers a wide area with its spreading 
branches. Also the Vitex agnus castus, planted in 
1550; and a superb palm, planted in 1585, and 
once visited and described by Goethe. This palm 
{Chamcerops humilis, var. Arborescens palmce, Af- 
rica) has had a house built about it to protect it 
from sudden changes of temperature, to which 
Northern Italy is subject. It is the most beauti- 
ful, graceful species of palm. It does not grow 
from one long trunk, crowned with its waving 
leaves; but just as the fronds of a fern spring 
from the ground, each one making its part of the 
beauty of the whole root, so does this palm, 
which, upspringing in twelve separate trunks, 
seems to shower its waving leaves about the 
mossy brown of the stems— the tallest being some 
thirty feet high and the lowest leaves witliin three 
feet of the ground. We were permitted to walk 
around the tree, and to get inside within the 
greenery and between the separate trunks. I 
regret much that it was not possible to obtain a 
photograph of it ; also of the Araucaria excelsa, a 
Conifera from Norfolk, Australia, 1829, in the hot- 
house near by, whose foliage— dense, yet ex(iui- 
sitely graceful— makes tlie tree worth a visit to 
Padua, were there nothing else of interest to be 
seen. There are several hot-houses, some of 
which were at such a temperature that — already 
overheated as we were— we dared not enter. In 
fact, the liouse where we found the Araucaria was 
intolerable, while that one next to it, where sev- 
eral varieties of the Pandanacem tlirive, — the ran- 
danus utilis, from Madagascar, 1850, the furcatis. 
reflexa, and elegatissium,— was at a higher degree 
of temperature still. Against tlie wall of this 
house was a dense growth of Ficus stipulate, 1850. 
Next to these most interesting trees, I was most 
impressed by the beauty and curious appearance 
of the Oingko bilatea, {Coniferce), from Cliina, 
1750, which flourishes in the open air. Tlie leaf, 
which is brilliant green in color, has the shape of 
the stone pine of Southern Italy. This resem- 
