Theophrasta 



( 388 ) 



Thinning 



is occasionally necessary when, in laying out large 

 estates, the heights of objects widely separated 

 have to be ascertained. In common levelling 

 operations the straightedge, borning rods, and 

 ordinary spirit level are enough. (See LANDSCAPE 

 GARDENING.) 



THEOPHRASTA. 



Stove shrubs (nrd. Myrsinese), of erect habit and 

 stately presence. Propagation, by cuttings of 

 semi-matured shoots, in a close case, with brisk 

 bottom heat. Soil, peat and loam in equal parts, 

 with sand. 



Principal Species : 



imperialis, Ap., yellowish grn., fruits like small 

 Apples. Ivs. 3' long, 10" broad, imposing. 



THERMOMETER. 



An instrument by which the degree of heat is 

 measured by the expansion of a ball of mercury or 

 a quantity of spirit enclosed in an hermetically 

 sealed glass tube. At the side of the tube is a 

 graduated scale by which the amount of expansion 

 is calculated. Prior to the sealing of the tube as 

 much air as possible is expelled, and the mercury 

 or spirit thus works in something that i's very 

 nearly a vacuum, so that there is no resistance to 

 the expansion. There are three " scales " by which 

 the expansion is calculated, in general use, viz. 

 Fahrenheit, which has the freezing point of water 

 at 32 and the boiling point at 212 ; Keaumur, 

 which has the freezing point of water at (zero) 

 and its boiling point at 80 ; and Centigrade, 

 which places the freezing point of water at 

 (zero) and its boiling point at 100. The Fahren- 

 heit scale is the one generally adopted in this 

 country. 



A minimum and maximum registering instru- 

 ment is needed for meteorological observations 

 outdoors. The maximum and minimum are ob- 

 tained by means of a sensitive needle which is 

 pushed up or down by the mercury, and left to 

 mark the extreme limit of the rise or fall of the 

 temperature. This needle is " set" to the mercury 

 by means of a magnet. Outdoor thermometers 

 should be fixed to a stout post about 4' from the 

 ground, should face towards the north, and be 

 covered in by a box or screen, so as to give the 

 "shade" reading. The height of the glass with 

 the sun full upon it is not a true index to the 

 general temperature. 



There should be a thermometer placed in each 

 glasshouse, and it is an excellent plan to affix to it 

 a little celluloid tablet, upon which to mark the 

 degree of heat to be maintained in the house as a 

 guide to the stoker. (See also TEMPERATURES.) 



Special plunging thermometers are made for 

 ascertaining the temperature of Mushroom and 

 hotbeds. A stick is more commonly used in 

 practice, and although a rough-and-ready test it is 

 usually sufficient for the practical man. (For wet 

 and dry thermometers, see HYGROMETER.) 



THERMOPSIS (syn. THERMIA). 



Hardy perennial herbs (ord. Leguminosae). Mon- 

 tana is a gem for nooks in the rockery, and looks 

 at its best when rising among dwarf plants. Prop- 

 agation, by seeds. The roots do not take kindly 

 to division. Soil, light, rich loam, in a sheltered 

 situation. 



Theresia (gee Fritillaria). 



Principal Species :- 

 barbate, 1', Je., hdy., 



deep pur., stems 



woody. 

 corgouensis, 2', sum., 



hdy., yel. 

 lanceolata, 1', sum., Sidy., 



vel. ((/. Podulyria 

 lupiuoides). 



montaua, 2', sum., hdy., 

 yel. (SI/H. t'abacea of 

 Hooker). 

 uepaleusis {see Piptanthus 



nepalensis). 

 THEROPOGON. 



A greenhouse perennial herb (prd. Liliaoeas), 

 with Grass-like leaves. Propagation, by seeds, 

 sown in heat, in spring, and by root division. 

 Soil, light sandy loam. 

 Only Species : 

 pallidus, spr., grh., wh., sometimes flushed pk. 



THESIUM. 



Stove, greenhouse, and hardy herbs (nrd. Santa- 

 lacea?), of no decorative value. A few of them 

 have been introduced, but are not now in culti- 

 vation. 



THESPESIA. 



Stove trees and tall-growing herbs (ord. Malva- 

 ceae), not well known to gardeners, although the 

 flowers of some of the species are showy. Prop- 

 agation, by ripe cuttings, in sand, in bottom heat. 

 Soil, loam and peat in equal parts, with sand. 



Principal Species and Variety : 

 grandirlora, 30', st., My., spot, finally all pur. 



red ; close to populuea Mahoe, Portia-nut Oil 



in habit. Plant, Umbrella Tree. 



populuea, 40', St., Je., - guadalupeusis, petals 



yel., with ceutral pur. uarrower. 



THEVETIA. 



Stove shrubs or small trees (ord. ApocynaceEe), 

 little known to gardeners. Propagation, by cut- 

 tings, in sand, in a close frame, with bottom heat. 

 Soil, fibrous loam three parts, leaf mould one part, 

 and sand. 



Principal Species : 

 Ahouai, 20', Je., st., yel. vetia). Exile Oil 



(.//. Cerbera Ahouai). Plant. 



neriifolia, 12', st., Je., Yccotli, 8', st., close to 



yel. (syn. Cerbera The- ueriifolia, fruits like 



small Apples. 



THIBAUDIA. 



Stove shrubs (ord. Vacciniaceos), many of which 

 are now referred to Agapetes, Cavendishia, and 

 Pentapterygium (which see). Propagation, by cut- 

 tings, in sand, in a close frame. Soil, sandy peat. 

 Both the species named are elegant plants, deserv- 

 ing a place in the stove. 



Principal Species : 

 floribunda, st. or warm pichinchensis, 6' to 12', 



grh., sc., Ivs. leathery, sc., Ivs. oval. 



oblong, lanceolate. 



THINNING. 



The timely thinning out of superfluous plants is 

 one of the vital points in the cultivation of annuals 

 of which seed has been sown where they are to 

 flower. If neglected a lot of spindly plants is the 

 result, and these rarely flower satisfactorily. Even 

 with thin sowing a subsequent thinning is essen- 

 tial. Half-hardy annuals receive their thinning 

 out at pricking off time. Kovvs of Carrots, Onions, 

 Parsnips, Beet, and other vegetables, have to be 

 thinned at an early stage, or the crop is irre- 

 trievably damaged. It should not be attempted 

 in dry weather, when the ground is hard, as the 

 plants would break off instead of coming out. 



