Biology Reference
In-Depth Information
Oedema
Potassium Deficiency
Small, wartlike, sometimes corky, excrescences
are formed on underside of leaves of many
plants - cabbage, tomatoes, geraniums, begonia,
camellias, etc. When roots take up more
water than is given off by leaves, the pressure
built up may cause enlarged mesophyll cells
to push outward through the epidermis. This
condition is rare outdoors but is found in
greenhouses and sometimes on house plants
where they have been overwatered. Copper
sprays sometimes produce similar intumes-
cences. Camellias frequently have corky swell-
ings on bottom surface of leaves, often due to
water relations, sometimes to a spot anthracnose
fungus.
Marginal browning, bronzing, or scorching
appears first on lower leaves and advances up
the plant, which is stunted. Leaves are often crin-
kled, curl inward, develop necrotic areas; the
whole plant may look rusty. The lack of potas-
sium can be made up with a complete fertilizer
containing 5 to 10 % potash. Wood ashes also
help to supply potassium.
Ring Spot
Yellow rings on African-violet foliage come
from breaking down of the chloroplasts when
the leaf temperature is suddenly lowered, as in
watering with water considerably colder than
room temperature.
Oxygen Deficiency, Asphyxiation
Rosette
Overwatered house plants and crops in poorly
drained low situations often show the same symp-
toms as those caused by lack of water, for the
roots cannot respire properly and cannot take up
enough water. Improve drainage; lighten soil
with compost and sand; avoid too much artificial
watering.
Zinc deficiency in pecan and walnut, boron defi-
ciency in apple.
“Rust”
This term is used by amateur gardeners for any
rust discolorations - for a leaf blight of phlox of
unknown origin (probably a water relation),
a spot necrosis of gladiolus, red-spider injury,
and many other troubles that have nothing to do
with true fungus rusts.
Phosphorus Deficiency
Young leaves are dark green; mature leaves are
bronzed; old leaves are mottled light and dark
green. In some plants there is yellowing around
leaf margins. Stems and leafstalks develop red-
dish or purplish pigments; plants are stunted,
with short internodes; growth is slow, with
delayed maturity. Most complete commercial
fertilizers have adequate phosphorus, but it can
be added separately in the form of superphos-
phate. In preparing rose beds apply a liberal
amount at the second spade depth as well as in
the upper soil.
Salt Injury
Trees and shrubs along the seacoast are injured by
ocean spray, and after hurricanes and high winds
traces of injury can be found 35 to 40 miles
inland. Conifers are usually affected most; they
appear damaged by fire, with needles bright yel-
low, or orange-red. Eastern white pine is very
susceptible; Austrian and Japanese black pines,
blue spruce, and live oak are highly resistant.
