AN ENCYCLOPAEDIA OF HORTICULTURE. 



255 



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 larvae, see Insects, 

 Surface Caterpillars, and Tiger Moth. The Let- 

 tuce Fly (Anthomyia Lactuccs), 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 in. long when full grown. In the 

 Lettuce head, or on the ground, they turn to pupae, 

 oval in form, and red-brown in colour. The flies emerge 

 from the pupae 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 bo dis- 

 eased, the whole crop should be carefully looked over, 

 and the larvae 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 shoots, 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. Soaking 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 plants should be speedily 

 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 

 that may remain in the soil. Attacks may, perhaps, 

 be prevented by surface-dressings of soot, lime, or other 

 substances disagreeable to insects. Both species live also 

 upon the roots of various grasses and other plants ; hence 

 it is difficult to eradicate them. 



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 Composites, since they also are food-plants 

 of this Mildew. 



LETTUCE FLT (Anthomyia Lactucce). 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 pupae 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 pupae. Infected crops, 

 when cleared off the ground, should be burned. 



LETTUCE, LAMB'S. See Corn Salad. 

 LEUCADENDB.ON (from leukos, white, and dendron, 

 a tree ; the Wittebroom, or Silver-tree of the Cape 

 colonists). OBD. Proteacece. 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, fl. yellow, in terminal 

 heads, and of but little beauty. August. 1. closely set upon the 

 stems, lanceolate, 4in. to 6in. long, lin. broad, of a very beautiful 

 silvery white, h. 15ft. 1693. A very handsome tree, too rarely 

 seen in cultivation. The dried leaves are imported, and largely 

 used in the making of wreaths, &c. (B. R. 979.) 

 LEUCADENDRON (of Salisbury). A synonym 

 of Leucospermum (which see). 



LEUCHTENBEB.G-IA (named after Prince Leuch- 



tenberg). OBD. Cactece. A monotypic genus, the species 



being a greenhouse succulent. Flowers produced at the 



top of the plant, among the younger mamillae, 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. 



L. principls (princely), fl. rich clear yellow, large, usually soli- 



tery, produced near the axils of the tubercles. 1. flaucous 



green, succulent, 4in. or 5in. long, triangular, truncated at the 



apex, and there bearing six or seven long chaffy, or almost horny 



linear or subulate flexuose scales, of which the centre one is 



almost as lone as the mamillae, and the others form a whorl 



round the centre. Stem about as thick as a man's arm, hard and 



woody covered with the remains of decayed mamillae. Mexico, 



1847. (B. M. 4393.) 



LEUCOCAB.FUS (from leukos, white, and karpos, a 

 fruit ; alluding to the colour of the berries). OBD. Scrophu- 

 larinece. A monotypic genus, the species being a tall, 



