330 
AMERICAN AGRICULTURIST. 
[July, 
Stone Bridges. 
The most durable bridges are made of 
stone, which is preferable to wood for this 
purpose, even if the expense is one-third 
greater. A small, well-built stone bridge 
will last for at least fifty years, wdiile one of 
wood will need renewing twice in that 
period, to say nothing of occasional repairs. 
When a stone bridge is out of repair, it is 
only necessary to readjust the displaced 
stone ; with a wooden structure, the decayed 
portions are, for the purpose of repairing, 
worse than useless. For streams, where the 
water, during the heaviest freshets, will all 
pass through an opening three feet wide and 
two feet high, stone bridges should be'built. 
Larger bridges of this material are frequently 
met with, but they are expensive, especially 
if flat stones for covering are difficult to ob¬ 
tain. A section of a bridge, constructed 
wholly of flat stone, is shown in the engrav¬ 
ing. When it is difficult to obtain stones 
wide enough to cover the top, let a course of 
flat stone, along each side, project inward 
ing. They will, with the greatest ease, cany 
heavy riders up the steepest ascent. The 
Poitou donkey is the most square built and 
strongest; the Gascon is taller, slighter, and 
of a more elegant shape. Some of the notable 
points of the former are a thick frizzled coat, 
long hair on the legs, from the knee down, 
and a thick growth of the same inside and 
around the ears. This is supposed to indi¬ 
cate strength of constitution, and there may 
be something in the claim that long thick 
hair preserves the donkey’s skin from ce 
tain diseases. The best stallions are worta 
from 3,000 to 4,000 francs ($600 to $800). 
Donkeys of the smaller breeds may be had 
for from $40 up to $50 each, but such are 
not worth importing into the United States. 
We want only the largest and best, and it is 
most profitable to breed from these alone. 
CROSS-SECTION OF A STONE BRIDGE. 
from six to ten inches, as at a, a, and cover 
with the widest stone, as at b, laying on a 
course of smaller ones, to prevent earth from 
sifting through. A stone or small wooden 
bridge covered witli eighteen inches of 
earth, will outlast one having a covering 
of but six inches. Add to the depth of cov¬ 
ering, even if necessary to elevate it above 
the road-bed at the sides. Lay a wall, or 
place large boulders at the upper end of the 
bridge, outside the channel, to prevent the 
embankment from washing away. When 
the bridge is over a rapid stream or on a side 
hill, it is best to cover the bottom of the 
channel with stone. This should be done 
when building, and consists in placing flat 
stones at the lower end of the bridge, letting 
the stone wall rest upon them, or at least 
press firmly against them. One flat stone 
overlaps the one below, shingle fashion. 
Plank may be used instead of stone, being 
placed after the wall is laid, and the ends 
fastened by pins to a sill imbedded in the 
soil at each end. 
The Stems of Plants. 
An examination of the structure of a 
plant stem of any kind shows that woody 
tissue, in some form, is an indispensable con¬ 
stituent. Its arrangement and nature varies 
greatly, but it is always present in the mature 
stem, although in many cases it would hardly 
be recognized as such. This variation in the 
arrangement of the wood has been made the 
basis for a division of stems into two great 
classes. In one the wood is in concentric 
rings around the pith, and is itself surrounded 
by a layer of bark. Each year’s growth 
forms a new ring of wood outside that of the 
year previous, and completely enclosing it. 
Hence such stems are called exogens, or out¬ 
side growers. This structure is easily seen 
in any so-called woody plant, and is typified 
in our Northern forest trees. Figure 1 is a 
cross-section of such a stem, of three years’ 
growth. The other class produces its wood 
in the form of isolated fibres or threads, sur¬ 
rounded by pith. The new wood, or fibres, 
appears in the center of the stem, reaches 
maturity in the first year, and never in¬ 
creases in thickness afterward. Such stems 
produce no bark, and have no separate pith, 
it being interspersed among the woody fibres. 
French Donkeys are among the largest, 
finest, and most powerful known. The best 
are bred in the provinces of Poitou and Gas¬ 
cony. They are the sires which produce, out 
of large sized mares, the superior mules 
one finds in Switzerland for mountain climb¬ 
Fig. 1.— SECTION OF EXOGENOUS STEM. 
They are called endogens, or inside growers, 
and include all the grains and grasses. The 
best example for observation is a corn-stalk, 
in which the woody fibres are readily seen 
by the naked eye. Figure 2 represents a 
cross-section of the same, showing several 
of these woody fibres. 
The office of the stem, in relation to the 
life of the plant, is to convey the sap from 
the roots to the leaves, and, after it has been 
digested by light, oxygen, and carbonic acid, 
to the various parts of the plant where 
growth demands it. The flow of sap from 
the roots to the leaves always takes place in 
the newer or sap-wood. The heart-wood, 
from its density and low vitality, conveys 
only a little sap ; and this part of the stem 
Fig. 2.— SECTION OF ENDOGENOUS STEM. 
has no very important share in the work 
of the plant, save to strengthen the more 
active regions. This is shown by the fact' 
that the vital operations go on undisturbed 
after the heart-wood has entirely disappear¬ 
ed. But the stem not only carries crude ma¬ 
terials to the leaves, but distributes the plant 
food which is there prepared. The elab¬ 
orated sap turns back from the leaves, along 
the branches to the stem, and all parts of 
the plant where it is needed in producing 
new growth. The inner, soft layer of the 
bark, is the most highly vitalized portion of 
the stem, if not of the whole plant, and it is 
here that new growth always takes place. 
From a physiological standpoint, the most 
important parts of the stem are the sap-wood 
and the inner layer of the bark. We have 
spoken of these regions as they occur in our 
woody plants of the class of outside grow¬ 
ers, but each woody fibre of the inside 
grower has corresponding regions which per¬ 
form a similar function. The same general 
laws apply to both exogenous and endoge¬ 
nous stems. 
Besides acting as a conduit for the passage 
of sap, the stem bears aloft into light and 
air such parts of the plant, as the leaves and 
fruit, to which these conditions are neces¬ 
sary. It may also serve as a storehouse, 
especially in its modified forms, for reserve 
plant food. Starch is usually found, often 
abundantly, while the presence of sugar in 
various trees in the spring time is well 
known. 
Certain forms of stems are so much dis¬ 
guised, that at first they would hardly be re¬ 
garded as such. The potato, for instance, is 
an extreme form, and its eyes are really buds. 
The scaly, root-like growth of the Couch or 
Quick Grass is simply an underground stem, 
and its rapid propagation is due to the fact 
that each scale protects a well-developed bud. 
Other curious modifications are well known. 
The beauty of our landscapes, the adorn¬ 
ment of our homes, and the applications of 
our arts and manufactures, depend upon the 
infinite variety of form and structure dis¬ 
played in vegetable stems. 
Profes or Henry, in his report of the 
experiments in amber cane at the university 
farm, Madison, Wis., states that a sandy soil 
is best adapted to cane-growing. It is warm¬ 
er than any other, and no crop cultivated at 
the North ‘ ‘ revels in heat as does the sor¬ 
ghum plant.” The cane roots run deep into 
the soil, and thrive where the comparatively 
shallow-rooted corn would dry up and make 
only a stunted growth. A second advantage 
is, that sandy soil does not contain a large 
