' harm already done. 
526 
THE DICTIONARY OF GARDENING, 
Sun-burning—continued. 
the result; but it is impossible to determine the share 
due to each. A very rapid rise of temperature, after 
severe cold, is also apt to produce results included 
under the general name of Sun-burning. 
Most plants, if exposed for some time to a temperature 
between 105deg. and 125deg. Fahr., are killed; but cer- 
tain fleshy subjects, particularly species from tropical 
deserts, are able to resist even a higher temperature 
than 125deg. When plants that have been in a green- 
house all the winter are first put out of doors, in spring, 
the leaves often become brown and look scorched. These 
organs may die and wither, or may only become red or 
brown, and afterwards reassume their natural green 
colour. Plants do not usually suffer serious injury from 
this cause, though often checked in their growth for 
a time. 
In ill-ventilated glasshouses, it often occurs that thé 
leaves of many of the plants show round, pale, withered 
spots. Observation teaches that these follow the pre- 
sence on the leaves, during sunshine, of drops of water; 
and it has been suggested that the drops act like minia- 
ture burning-glasses, focussing the rays upon the spots 
below them, and destroying the protoplasm by the excess 
of light and heat so caused. Inequalities in the glass 
of greenhouses are believed to give rise to similar 
injuries. Whatever may be the cause, experience has 
proved that thorough ventilation is the best preventive, 
and that, if this is attended to, the evil will be much 
diminished, if not wholly cured. 
Sun-burning and Sunstroke are terms applied to in- 
juries of the stems of trees, consisting sometimes in the 
bark dying, and separating from considerable surfaces, 
or in long strips, on the side most exposed to the sun’s 
rays. Sunstroke is apt to occur in trees exposed by the 
removal of others or of undergrowth, or it may follow 
the erection of walls or other reflectors of heat in the 
immediate neighbourhood of the stems. It injures both 
fruit-trees (especially Peaches) and forest-trees when 
suddenly exposed. The cause of injury is the death of 
the newly-formed cells of the cambium layer by exposure 
to excessive heat. In trees suddenly exposed to varia- 
tions in temperature greater than they had previously to 
bear, the bark is not sufficiently developed to protect 
the cambium from injury, and the result is as just de- 
seribed. ; 
Splitting of the bark is apt to occur in spring, when 
trees have been exposed for some time to keen frost, 
followed by a sudden rise of temperature. The injury 
is due to unequal expansion of the bark and the wood. 
Probably, it is more often caused by the preceding frost 
than by the warmth, the thaw only bringing to view the 
But that Splitting is, to some 
extent, connected with the suns warmth is shown by 
its greater frequency on the side of the trunk that 
receives most of the sun’s rays. Both Sun-burning and 
Splitting are far commoner on the Continent than in 
Britain, where the extremes of heat and cold are 
seldom such as to give rise to either. The best pre- 
 ventive of both is to protect the trunks and branches 
that may be in danger, by some simple means of shelter, 
such as ee them in straw, or coiling a straw-rope 
em. 
A few years ago, Dr. H. Müller, of Thurgau, called 
attention to the loss of grapes that occurs in various 
places in Germany when cold, damp weather is sud- 
denly followed by bright, warm, sunny days. In the 
unripe clusters that are exposed to the direct rays of 
the sun, many of the grapes become pale, and then 
shrivel and turn brown. Sometimes, the stalks of the 
clusters turn brown before the grapes show signs of 
injury, but the latter soon shrivel and die when the 
stalks are killed. Experiments show that the cause of 
injury is excessive heat, and that similar results follow 
Sun-burning—continued. 
when clusters are exposed to artificial heat as great as 
that to which they are subjected under natural condi- 
tions, i.e., between 105deg. and 1lideg. Fahr. The risk 
of injury is greater in proportion as the fruit is more 
| juicy. The moister the atmosphere, the less must be the 
evaporation from the fruit; hence, in moist weather, 
evaporation cannot act as a means of keeping down the 
temperature, and this probably explains how the harm 
done is greater after a continuance of wet weather, as 
the air is then nearly saturated with moisture. The risk 
is much less in England than in Germany, as the tem- 
perature is seldom so high in our islands as to do injury. 
Prevention may be secured by any method of shading 
the clusters. The best protection is that afforded by the 
leaves of the Vines themselves; hence, the removal of 
the leaves to hasten ripening is seldom to be recom- 
mended. 
Though not strictly included under Sun-burning, a 
few remarks may be added on the harm done by dry, 
windy weather to many plants that grow in moist soil. 
If exposed for some days to dry, warm. winds, the leaves 
of such plants wither and die, becoming so brittle as to 
crumble into dust when rubbed in the hand. Under 
similar conditions, the same species of plants growing in 
_ drier ground may scarcely be injured. The cause is as 
follows: The damper the localities in which plants grow, 
the more are all their green parts adapted for rapid 
evaporation, While the evaporation is balanced by the 
amount of water absorbed by the roots, and carried up 
by the stems, growth goes on rapidly, and the plants 
grow luxuriantly, unless the mineral matters absorbed 
with the water accumulate to a hurtful degree, when — 
the plant will become weak and sickly. But in dry, 
warm weather, the loss by evaporation exceeds the 
amount that can be supplied to the leaves; hence, they 
wither, and dry up. Those that suffer most are the 
mature leaves in the active discharge of their functions, 
the older and younger ones being far less severely 
injured. The only remedial means applicable is to 
shelter the choicer plants from wind and sunshine as 
much as possible, and to syringe their leaves occasion- 
ally. Watering the soil is of no use, as it is already 
too moist. On such ground, drainage is the most 
efficient means of preventing injury to the plants from 
drought. 
SUNDEW. See Drosera. 
SUNDROPS. A name applied to (nothera fruti- 
cosa. 
SUNFLOWER. A popular name for the species 
and varieties of Helianthus, but more particularly applied 
to the varieties of H. annuus, which may readily be 
raised from seed each year. Sunflowers are best adapted 
for planting at the back of large shrubbery borders 
or in wild gardens. 
SUNIPIA (said to be the native name in Nepaul). 
ORD. Orchidee. A monotypic genus. The species—a 
stove, epiphytal orchid, with small, racemose flowers, 
lateral, elongated, leafless scapes, and a coriaceous, slen- 
der, many-veined leaf—is a native of Java, and awaits 
introduction to this country. 
SUN-PLANT. A popular name for Portulaca grandi- 
flora and other species. 
SUN ROSE. See Helianthemum. 
SUPERIOR. Growing above anything. The pos- 
terior or upper lip of a corolla is the Superior. “A calyx 
is Half-superior when it appears to grow from above 
the base of an ovary, and absolutely Superior when it 
appears to grow from the top of the ovary. On the 
contrary, the ovary is Superior when it grows above 
the origin of the calyx” (Lindley). 
