LAYER 



490 



LEAVES 



Greenhouse herbaceous perennials, from Australia. 

 Divisions ; loam and peat ; require a cold pit or cool 

 greenhouse during winter. 



L. gra'cilis (slender). . Purple, white. June. 1824. 

 ,, grandiflo'ra (large-flowered). White, brown. 



LAYER. The following excellent combination of 

 practice and science is from Dr. Lindley's Theory of 

 Horticulture : A layer is a branch bent into the earth, 

 and half cut through at the bend, the free portion of 

 the wound being called " a tongue." It is, in fact, a 

 cutting only partially separated from its parent. The 

 object of the gardener is to induce the layer to emit roots 

 into the earth at the tongue. With this view he twists 

 the shoot half round, so as to injure the wood- vessels ; he 

 heads it back, so that only a bud or two appears above 

 ground, and when much nicety is requisite, he places a 

 handful of silver-sand round the tongued part ; then, 

 pressing the earth down with his foot, so as to secure the 

 layer, he leaves it without further care. The intention 

 of both tonguing and twisting is to prevent the return of 

 sap from the layer into the main stem, while a small 

 quantity is allowed to rise out of the latter into the 

 former ; the effect of this being to compel the return- 

 ing sap to organise itself externally as roots, instead of 

 passing downwards below the bark as wood. The bend- 

 ing back is to assist in this object by preventing the 

 expenditure of sap in the formation, or rather, completion 

 of leaves, and the silver-sand is to secure the drainage so 

 necessary to cuttings. 



In most cases this is sufficient ; but it must be obvious, 

 that the exact manner in which the layering is effected 

 is unimportant, and that it may be varied according to 

 circumstances. Thus, Mr. James Munro describes a 

 successful method of layering brittle-branched plants by 

 simply slitting the shoot at the bend, and inserting a 

 stone at that place (Gardener's Magazine, ix. 302) ; 

 and Mr. Knight found that, in cases of difficult rooting, 

 the process is facilitated by ringing the shoot just below 

 the tongue about Midsummer, when the leaves upon the 

 layers had acquired their full growth (Hort. Trans., i. 

 256) ; by which means he prevented the passage of the 

 returning sap farther downwards than the point intended 

 for the emission of roots. It will sometimes happen that 

 a branch of a plant cannot be conveniently bent down- 

 wards into the earth ; in such cases, the earth may be 

 elevated to the branch by various contrivances, as is 

 commonly done by the Chinese. When this is done, no 

 other care is necessary than that required for layers, 

 except to keep the earth surrounding the branch steadily 

 moist. 



LA'YIA. (Commemorative of Thomas Lay, the natura- 

 list who accompanied Beechey in his voyage. Nat. ord. 

 Compositae.) 



Hardy annuals that might more often be cultivated. 

 Seeds in the open in April. Ordinary garden soil. 

 L. calliglo'ssa (beautiful- tongued). i^. Yellow. August 



and September. N.W. Amer. 



chrysanthemoi'des(Chyrsznthemum-]ike). i. Yellow, 

 with paler tips. September. N.W. Amer. 1834. 

 Dougla'sii (Douglas's), i. Yellow. N.W. Amer. 

 ,, e'legans (elegant), i. Yellow, tipped white. June to 



September. California. 1883. 

 gaillardioi'des (Gaillardia-like). 1-2. Orange- yellow. 



California. 1902. 

 glandulo'sa (glandular), i. White, with yellow disc. 



California. " Tidy Tips." 



,, Hetero' tricha (various-haired). White. California. 

 platye,lo'ssa (flat- tongued). i. Yellow. September. 

 California. 1836. 



LAYING-IN is a gardener's term for training the 

 branches of espaliers and wall- trees. Laying-in-by-the- 

 heels is his mode of describing a plant's having its roots 

 roughly buried in the soil for some temporary purpose. 



LAYING-IN. Fruit-trees, shrubs, roses, and other 

 plants from the nursery often arrive at a time when they 

 cannot be properly planted, owing to the ground being 

 too wet or frozen, or if numerous and require some time 

 to plant, the gardener resorts to the practice of laying 

 them in. A trench is made, and the plants are laid in a 

 slanting direction in the trench, and their roots covered 

 with soil. In severe weather they may also be covered 

 with mats. The stems of roses are sometimes shrivelled 



on arrival, owing to delay since they were lifted. In 

 that case a deep trench is made and the roses laid in the 

 bottom of it, and entirely covered with soil for a week or 

 more till they become plump. This is burying them 

 temporarily. 



LAZY-BEDS are beds dug for the growth of potatoes, 

 the sets being then placed in rows on the surface, and 

 covered by the soil dug out of narrow, deep alleys 

 between the beds. 



LEADWORT. Plumba'go. 



LEAF-MOULD. This is formed of leaves kept moist 

 and in a heap, frequently turned over, until completely 

 decayed, and reduced to a dark brown, moist powder. 

 It usually takes two years to complete this process. An 

 excess of water delays the decaying, and either lime or 

 gas ammoniacal liquor promotes it ; but then few potted 

 plants are benefited by any such excess of either of these 

 additions. 



LEATHERWOOD. Di'rca. 



LEAVENWO'RTHIA. (Commemorative of M. C. 

 Leavenworth. Nat. ord. Cruciferae. Allied to Arabis.) 



Dwarf, annual herbs with leafless scapes. Seeds. 

 Ordinary garden soil. 

 L. au'rea (golden). See L. MICHAUXH. 

 Michan'xii (Michaux's). . Yellow. June. N.W. 

 Amer. 1868. 



LEAVES are the organs, in which are performed some 

 of the most important functions of a plant. They are 

 very general, but not absolutely necessary organs, since 

 the branches sometimes perform their offices, as in Cacti, 

 Asparagus, Butcher's Broom, and many others. Such 

 plants, however, as naturally possess them, are destroyed, 

 or greatly injured, by being deprived of them. 



The duration of a leaf is, in general, for a year only, 

 though in some evergreens they survive for twice or 

 thrice that period. These organs are generally of a 

 green colour. Light seems to have a powerful influence 

 in causing this, since, if kept in the dark, they become 

 of a pale yellow, or even white hue, unless uncombined 

 hydrogen is present, in which case they retain their 

 verdure though light be absent. Hence their blanching 

 would seem to arise from their being unable to obtain 

 this gas under ordinary circumstances, except when light 

 is present. Now, the only source from which they can 

 obtain hydrogen is by decomposing water ; and how 

 light assists in the decomposition, may, perhaps, be ex- 

 plained by the dis-oxygenising power with which it is 

 gifted. The violet rays of the spectrum, and those just 

 beyond them, have this power in the greatest degree ; 

 and Sennebier has ascertained by experiment that those 

 rays have the greatest influence in producing the green 

 colour of plants. 



When leaves are of any other hue than green they are 

 said to be coloured. This variegation is often considered 

 to be a symptom either of tenderness or debility ; and 

 it is certain, when the leaves of a plant become generally 

 white, that that individual is seldom long-lived. Mr. 

 Knight, however, has demonstrated that variegation is 

 not a certain indication of a deficiency of hardihood. 



The functions of the leaves appear to be a combination 

 of those of the lungs and stomach of animals ; they not 

 only modify the food brought to them from the roots, 

 so as to fit it for increasing the size of the parent plant, 

 but they also absorb nourishment from the atmosphere. 

 The sap, after elaboration in these organs, differs in 

 every plant, though, as far as experiments have been 

 tried, it appears to be nearly the same in all vegetables 

 when it first reaches them. The power of a leaf to 

 generate sap is in proportion to its area of surface, 

 exposure to the light, and congenial situation. 



The transpiration of plants decreases with that of the 

 temperature to which they are exposed, as well as with 

 the period of their growth. This explains why the 

 gardener finds that his plants do not require so much 

 water in cold weather, nor during the time that elapses 

 between the fall of their blossoms and the ripening of 

 their seed. During this period they do not transpire 

 more than one-half so much as during the period preceding 

 and attending upon their blooming. 



The transpiration takes place chiefly from the under 



