he'dera. 



] 



3S 



HEDGEHOGS. 



they are very apt to damp off if the soil 

 in "which they grow has not been 

 well drained. The best varieties are 

 propagated by cuttings taken off from 

 the points of the shoots, in the spring, 

 cutting them clean across immedi- 

 ately below a joint. The cuttings 

 should be struck in pure white sand, 

 and covered with a bell-glass ; they 

 should not be watered when put in, 

 and they should be shaded for several 

 days. Heart' s-eases are also propa- 

 gated by layers, pegged down at a 

 joint, but not slit, on account of their 

 tendency to damp off. 



Heat is concentrated or produced 

 in gardens in a variety of ways : by 

 shelter from winds, which prevents 

 the natural heat of the plants from 

 being carried off by currents of air pass- 

 ing over them ; by exposure to the sun, 

 which concentrates its rays ; by cover- 

 ing a surface of soil, or the roots and 

 stems of plants with a non-conducting 

 material, such as straw, litter, leaves, 

 &c. which prevents its radiation ; by 

 fermenting substances, such as stable- 

 dung, litter, leaves, tan, &c, which 

 produce heat by their decomposition ; 

 and by the consumption of fuel, from 

 which the heated air generated, is con- 

 ducted in fiues, or by means of pipes 

 of hot water or steam. Hot-beds are 

 generally heated by a bed of horse- 

 dung, or other fermenting material; 

 and brick -built pits, or houses with 

 glass roofs, are heated by furnaces and 

 flues, or furnaces,boilers, and pipes of 

 hot water or steam. Stable-dung and 

 hot- water-pipes are the two best modes 

 of heating pits and glass-roofed houses. 

 Heat when produced is retained by 

 coverings which admit the light, such 

 as glass sashes, or in some cases frames 

 covered with oil-paper, or with very 

 thin canvas or gauze. 



Heath See Ertca. 



He'dera. — Araliacece. — The Ivy. 

 This well-known plant is what bota- 

 nists call a rooting climber ; that is to 



say, its stems climb up and twine 

 themselves round trees, or any other 

 suitable object which presents a suffi- 

 ciently rough surface for their roots to 

 take hold of; as, unless this is the case, 

 the ivy,Avhenever it is rendered heavy 

 by rain or snow, falls down. Whenever, 

 therefore, ivy is wanted to cover smooth, 

 newly-plastered walls, trellis-work 

 should be fixed against them, to 

 which the ivy should be nailed like 

 any other plant. The ivy is remark- 

 able for undergoing a complete change 

 in its leaves when it flowers. The 

 barren or creeping ivy, which trails 

 along the ground, and roots into it, 

 rarely flowers, and its leaf is deeply 

 cut ; but the tree ivy, or flowering 

 part, rears itself on high, so as to be 

 fully exposed to the light and air, and 

 the leaves become of an oval shape. 

 H. canariensis, the giant, or Irish ivy, 

 as it is sometimes called, though it is 

 a native of the Canaries, is hardier 

 and grows much faster than the 

 common kind ; but the variegated 

 kinds are more tender, and grow much 

 slower. Ivy requires a deep and 

 somewhat light soil, into which its 

 roots can penetrate easily ; and when 

 grown for any purpose in pots or 

 boxes, it should be abundantly sup- 

 plied with water. Ivy is useful in all 

 cases where a naked space is to be 

 covered with green in a short space of 

 time ; and it is particularly valuable 

 in town gardens, as it will bear the 

 smoke and want of pure air in cities 

 better than most other plants. It 

 should, however, in all close and 

 crowded situations, be abundantly sup- 

 plied with water, and occasionally 

 syringed over the leaves. The gold 

 and silver varieties are very beautiful, 

 especially the former, when grown 

 against the chimney of a dwelling- 

 house or hothouse ; but they require 

 warmth to make them thrive. 



Hedgehogs. — Medicago minima. 

 — An annual plant, with small yellow 



