nnr. ]. 
J ²˙ ü 
AN ENCYCLOPADIA 
OF HORTICULTURE. 955 
Lettuce—continued. 
The leaves are devoured by the caterpillars of not a few 
of the larger Moths, including the Tiger Moth (Arctia 
Caja) and its allies, and the genera Agrotis, Noctua, 
Mamestra, Plusia, and other thick-bodied night moths. 
For the methods of destroying such larve, see Insects, 
Surface Caterpillars, and Tiger Moth. The Let- 
tuce Fly (Anthomyia Lactuce), in the maggot stage, 
feeds on the fruits, eating out the seeds, and thereby 
destroying the harvest when plants are grown for seed. 
The maggots are footless, tapering near the head, trun- 
cate and toothed at the tail, dirty yellowish-white, 
and a little over fin. long when full grown. In fhe 
Lettuce head, or on the ground, they turn to pupae, 
oval in form, and red-brown in colour. ‘The flies emerge 
from the pups in early summer. They are about the 
size of a house-fly, and are rich brownish-black, with 
brown wings. Infected seed should not be used for 
sowing; and, as soon as the plants are seen to be dis- 
eased, the whole crop should be carefully looked over, 
and the larve removed, or, if not worth this trouble, 
the plants should be burned, to destroy the maggots. 
Aphides, or Green Flies, of several species, feed on 
Lettuces, two or three kinds of Siphonophora feeding 
on the leaves and young po and species of the genus 
Pemphigus dwelling on the roots. The latter are far 
more hurtful than the former, as they kill the roots, 
and thus destroy the plants. Pemphigus belongs to a 
group of Aphides that want the two tubes so con- 
spicuous in the others on the hinder segments of the 
back of the abdomen, and that have the cubital vein 
third from the body in the front wing not forked. 
The species hurtful to Lettuce are P. fuscifrons and 
P. lactucarius. Both live in cavities hollowed out of 
the soil beside the roots, and lined with fine cottony 
filaments secreted from the bodies of the insects. The 
second species is usually the more common and destruc- 
tive of the two, and forms the secretion more plentifully 
than the other. Prevention is difficult; nor is an 
attack usually suspected till the drooping of the plants 
indicates injury to the roots. The Aphides are generally 
found on scraping away some earth from the surface 
of the roots. ing the ground around the plants 
with soapsuds, lime-water, or tobacco-water, has been 
suggested as a remedy; but the gain would scarcely 
repay the cost. Infested 6 
and carefully removed, so as to destroy the Aphides 
on the roots; and the ground should have quicklime 
or gas-lime dug into it to destroy any of the pests 
Fungi. Of these, the most hurtful is the Lettuce 
Mildew (Peronospora ganglioniformis). Affected leaves 
show a yellowish discoloration on the upper surface, and 
on the lower surface there is a coat of fine white velvety 
threads, too small to be seen with the unaided eye. Under 
the microscope, the hairs are seen to be bifurcated from 
five to seven times, and each ultimate branch ends in a 
flattened dilatation, which bears four minute stalks on 
the corners, and one in the middle, each surmounted by 
an oval or nearly globular minute one-celled spore. In 
cold weather, in autumn, resting-spores are also produced 
in the tissues of the host plant. Their special use is to 
withstand the cold season, and to propagate the fungus 
when the weather becomes fit again to stimulate growth 
in spring. The velvety threads above described are 
pushed through the stomata, or little mouths of the plant. 
After a time, the patches of the leaf that bear the fungus 
begin to decay, and soon pass into a pulpy, rotten con- 
dition. The outer leaves are the first part affected, in 
Spring, while the flowers and seeds also frequently suffer 
Lettuce—continued. 
much in the autumn. The more crowded the Lettuce 
plants are, the more liable are they to injury from this 
fungus. If the plants are grown in a close, damp atmo- 
sphere, such as that in a frame for forcing them, in spring, 
or if weakened in any way, the Mildew does far greater 
mischief than where there is free access of air. Ex- 
posure of the plants to cold air has been found to mate- 
rially check an outbreak of Mildew; but the only method 
that can be relied upon is to remove the diseased plants 
as quickly as possible from among the healthy ones, 
taking care not to leave infected stumps of old plants in 
the ground. It is necessary also to keep the ground 
clear of Groundsel, Thistles, and other weeds belonging 
to the order Composite, since they also are food-plants 
of this Mildew. 
LETTUCE FLY en Lactuce). The larva 
is at times very destructive to the seed of the garden 
Lettuce. The eggs are laid on the flower, and the 
yellowish-white maggots bore into the seed-vessels, eat 
the seed, and then go on to repeat the process. They 
change into chestnut-brown oval pup in the flower-head, 
or in the ground, towards the end of September or in 
October. The flies appear in the next spring or summer, 
and are about the size of house flies. The female is 
grey, with a chestnut stripe down the face, and blackish 
legs. The male is black, with the face chestnut-brown; | 
four pale stripes on the front of the thorax; the rings of 
the abdomen grey, with dark base and triangular spot; 
legs black, and wings dark. 
Prevention. Care should be taken to insure that the 
seed, when sown, is free from pups». Infected crops, 
when cleared off the ground, should be burned. 
LETTUCE, LAMB'S. See Corn Salad. 
LEUCADENDRON (from leukos, white, and dendron, 
a tree; the Wittebroom, or Silver-tree of the Cape 
colonists). ORD. Proteacew. A rather large genus (about 
seventy species have been described) of woolly or gla- 
brous shrubs or trees, entirely confined to Southern 
Africa. Flowers greenish or yellowish, in heads at the 
tips of the shoots, sometimes rendered conspicuous by 
the large leaf-like coloured bracts which surround them. 
Leaves coriaceous, entire. The following is the most 
ornamental and best known species; several have been 
introduced, but very few are now in cultivation. 
L. argenteum (silvery).* Silver-tree. 44 yellow, in terminal 
set upon the 
AE A E Een 
silvery white. h. 15ft. 1693. Deti 
of 9 (which see). 
LEUCHTENBERGIA (named after Prince Leuch- 
tenberg). ORD. Cactee. A monotypic genus, the species 
being a greenhouse succulent. Flowers produced at the 
top of the plant, among the younger mamillw, very like 
those of Cereus, but having a more cylindrical perianth 
tube, and the stamens growing to its inside as far as 
the bottom of the petals, after which they converge and 
meet in the centre, closing up the mouth of the tube. 
The species, like most other succulents, require careful 
watering. For general culture, see Mamillaria. 
clear „ large, usually soli- 
e 
about as ode 3 hard and 
round the centre. b the of 3 arm, — 
LEUCOCARPUS (from leukos, white, and karpos, a 
fruit; alluding to the colour of the berries). ORD, Serophu- 
larinew. A monotypic genus, the species 
