« AnteriorContinuar »
roots are conical. Common quack grass, wood sage, and
peppermint produce numerous horizontal rootstocks that
are found close to the surface of the ground, 75 per cent
of the rootstocks being found within four inches of the
surface. From the nodes there arise numerous small
The roots of many perennial plants, like Canada thistle,
morning-glory, horse nettle, and milkweed, spread exten-
sively through the ground. The root of a common milk-
weed was traced by Mr. Garner and Mr. Lyle Clapper for
a distance of 14 feet through the soil.
Dr. Byron D. Halsted, who made a study of the roots of
various weeds, comments as follows concerning the char-
acter of roots: “By means of the root system most plants
become anchored to the soil; therefore, other things re-
maining the same, among those species that live from
year to year, the size of the root becomes an index of the
persistency and pestiferousness of the plant.” Then he
comments upon the length of roots of a great many
different weeds, stating that the common dandelion
(Tara.racum officinale) had a root an inch in diameter and
fifteen inches in length, but the writer has found a root
of the dandelion more than four feet in length. It should
be remembered also that in many cases when the root is
injured near the top that a multiple root development
follows. The burdock and dock frequently produce
numerous roots when the plants are injured, although
ordinarily these roots are straight and produce a single
thick fleshy root. The characters of roots sometimes
differ very materially in closely related species of plants.
The common sour dock has a straight fleshy root,
whereas the smooth or peach-leaf dock produces a num-
ber of branched roots, making it rather difficult to ex-
The following tables give the depth of roots and area
covered by some of the common weeds. These figures
RINDS OF WEEDS AS TO DUTRATION
indicate that the weeds may effectively rob the soil of
many valuable constituents.
*The roots of horse nettle extend straight down into the soil.
DISPERSAL OF WEED SEEDS
Scattering of Plants.-After the seed is formed it must be placed in a congenial soil so that its kind may be perpetuated. This scattering of seeds and fruits is therefore
important. The following are the different ways by which plants are scattered:
Fig. 5. Scattering of red cedar by birds. (U. S. Dept. Agri.)
A. Seed with light, inflated pods, Sedges.
B. In large receptacles, Nelumbo (Water Chinquapin).
C. Mucilaginous seeds, Pepper Grass.
D. Currents of water in a mechanical way, Driftwood.
E. Plants floating on water because provided with air spaces,
III. SNow AND WIND CoMBINED.
Many weed seeds.
A. Fleshy, edible fruits and seeds, Nightshade, Cherry
B. Edible seeds not fleshy, Sunflower, Acorn.
C. Fruits with hooks or barbs, Bidens (Beggar-ticks).
D. Seed or fruits with webs, Blue Grass.
Fig. 6. A tumble weed, winged pigweed (Cycloloma atriplicifolium), scattered by its tumble habit. The Russian thistle and a kind of pigweed are scattered in the same way. (U. S. Dept. Agrl.)
W. ExPLOSIVE PROPERTIES OF FRUITS AND SEEDS.
A. Contraction of seed vessel, as in Hura crepitans
B. Twisting of pod, Vetch.
C. Tension in pod, Impatiens (Jewel-weed).
D. Shooting of seeds, Oxalis.
E. Turgidity of fruit, Squirting Cucumber.
VI. Creeping MechANISMs AND BY THE SEEDS BURYING THEMSELVES.
A. Hygroscopic movements, Stipa.
B. Cleistogamous flowers, Violet.
VII. MAN AS AN AGENT.
A. Impure seed, Clover Dodder.
Common carriers, Russian Thistle.
Nursery stock and flowers, Canada Thistle.
Hay a.d wool, Buffalo Bur.
Plants grown for ornamental purposes, and as food plants,
Ox-eye Daisy, Chicory.
Wind.—Many of our weeds are scattered by the wind. The squirrel-tail grass, which is permitted to grow in an unobstructed manner in pastures and on roadsides, is car1 ied to adjacent fields where it did not occur. Tumbleweed and Russian thistle have the rolling habit, and when growing along the roadsides or the railway they get into adjacent fields. In prairie countries the tumble habit is common for many weeds. as shown many years ago Fig. 7. , Bull thistle “seed" scat- by Dr. Bessey. The seeds of tered by the wind. milkweed with a light fluffy * coma are carried for some distance. The “seeds” of dandelion with cylindrical body and a tuft of capillary bristles are carried for long distances from roadsides to fields and meadows. The bull thistle “seed” with hairy appendage is carried from the roadside to fields and pastures. Wind and Snow.—Many seeds glide over the frozen snow and become deposited in the field. Greater ragweed is frequently carried in this way. So, too, are the foxtails. Prof. H. L. Bolley states that January 20, he found in the contents of a snow drift of 28 square feet, 2 seeds of pigeon grass, 5 of French weed, 2 of biennial wormwood. and Io of barnyard grass. He also reports having distributed, on January 31, a peck of mixed seeds 30 rods distant from a drift of snow 4 rods long. In Io minutes this had caught a large number of millet, 191