HAWTHORN 



412 



HEAT 



SeeH. 



H. ni'gricans (granulated-black). See GASTERIA DECI- 



PIENS. 



ni'tida (shining). See GASTERIA NITIDA. 



obtu'sa (small-blunt). See H. CYMBIFORMIS OBTUSA. 



pa'llida (pale-green). . June. 1820. 



papillo'sa (nippled). i. June. 1820. 



semipapillo'sa (half-nippled). ii. June. 1820. 



pa'rva (small). See H. TESSELLATA. 



Peaco'ckii (Peacock's). 1879. 



Pearso'ni (Pearson's). J. Pale flesh, with brown ribs. 



1907. 



pili'fera (pile-bearing), $. Grey, green. 1862. 

 planifo'lia (flat-leaved). See H. CYMBIFORMIS PLANI- 



FOLIA. 



Polyphy'lla (many- leaved). 1860. 

 pseu'do-tortuo'sa (slightly-twisted-/nangw/<w). 



VISCOSA. 



pu'mila (dwarf-cobweb). See H. ATROVIRENS. 

 Ra'dula (file-surf aced-pearl). i. May. 1805. 

 aspe'rior (rougher), i. August. 1820. 

 Ice'vior (smoother), i. August. 1825. 

 pluriperla'ta (many-pearled), i. August. 1820. 

 rami'fera (branch-bearing). See H. ALBICANS. 

 recu'rva (curled-back-leaved). i. August. 1795. 

 Reinwa'rdtii (Reinwardt's pearl). J. June. 1820. 

 ma'jor (greater). 

 mi' nor (lesser). 

 reticula'ta (netted). J. June. 1794. 

 retu'sa (bent-back-cwsfo'on). i. June. 1720. 

 ri'gida (rigid). $-1. August. 1795. 

 rugo'sa (wrinkled). 1814. 

 sca'bra (rough). J. June. 1818. 

 semiglabra'ta (nearly-glabrous). J. June. 1811. 

 semimargariti'fera (half- pearl-bearing). See H. MAR- 



GARITIFERA SEMiMARGARiTiFERA and varieties. 

 sessilifio'ra (stalkless-flowered). S. Africa. 

 seta'ta (bristle-leaved), i. June. 1820. 

 ma'jor (larger), i. July. 1820. 

 me'dia (mediate), i. July. 1820. 

 ni'gricans (blackish), i. July. 1820. 

 seto'sa (bristly). See H. SET ATA. 

 so'rdida (sordid). |. July. 1820. 

 subattenud 'to, (slightly-elongated). 1814. 

 subfascia'fa (slightly-bundled). 1814. 

 subregula'ris (nearly-regular). . Grey, green. 1862. 

 subri'gida (somewhat rigid). J. Grey, tinted with 



pale red. 1818. 



subula'ta (awl-shaped). 1814. 

 tessella'ta (dark- checkered). J. June. 1823. 

 pa'rva (small). 

 Tis'leyi (Tisley's). 1879. 

 torqua'ta (collared). See H. VISCOSA. 

 torte'lla (slightly- twisted). See H. TORTUOSA. 

 tortuo'sa (twisted), i. July. 1794. 

 cu'rta (short- twisted), i. July. 1816. 

 translu'cens (transparent). |. June. 1795. 

 tu'rgida (swollen-ctts/on). J. August. 1819. 

 veno'sa (veiny). . June. 1820. 

 ,, vire'scens (greenish). See H. ALBICANS VIRESCENS. 

 ,, mi'nor (smaller). See H. ALBICANS MINOR. 

 ,, visco'sa (clammy), ij. June. 1727. 

 vitta'ta (striped). . Grey, green. 1862. 

 xiphiophy'lla (Xiphium- leaved). Leaves narrower 



and thinner than H. setata. 



HAWTHORN. Crata'gus. 



HAWTHORN BUTTERFLY. Aporia Cratagi. 



HAYLO'CKIA. (Named after Mr. Haylock, gardener 

 to Dr. Herbert. Nat. ord. Amaryllids [Amaryllidacea?]. 

 Allied to Cooperia.) 



A small bulb, with very narrow leaves and one flowered 

 scape. Offsets ; sandy loam, with a little peat and leaf- 

 mould ; requires the protection of a frame, or to be deeply 

 planted in a dry place in winter. 



H. pusi'lla (dwarf). J. Straw. September. Buenos 

 Ayres. 1829. 



HAYNAIDIA. (A commemorative name. Nat. oid. 

 Campanulaceae.) 



Greenhouse perennial. Divisions ; cuttings in sand 

 under a bell-glass. - Fibrous loam, leaf-mould, and sand. 

 H. thapsoi'dea (Thapsus-like). 6. Rosy-purple. Brazil. 

 1843. 



HAZEL. Co'rylus Avella'na. 



HEADING, or as it is also termed, Cabbaging or Leaving, 

 is an inaptitude to unfold the central leaves, character- 

 ising the various members of the Cabbage tribe. They 

 have their centre or bud composed of a larger number of 

 leaves than usual, and these, in some instances, are so 

 complexly combined that the plant has not sufficient 

 power to force them open to permit the protrusion of the 

 seed-stem. The closeness of the heading is regulated by 

 the exposure to the light. In a shady situation all the 

 leaves are required to elaborate the sap, on account of 

 the deficient light rendering each less active ; therefore 

 they open as they are formed. In a free exposure a few 

 leaves are able to effect the requisite assimilation ; and 

 hence the reason why cabbages always have " harder 

 hearts " in summer than in spring or autumn, when the 

 light is less intense. 



HEADING-DOWN, is cutting off entirely, or to a con- 

 siderable extent, the branches of a tree or shrub a 

 process not rashly to be resorted to, and adopted only 

 to reduce them when the plant seems declining in vigour, 

 or has attained an undesirable size. 



HEART'S-EASE. See PANSY. 



HEAT is the prime agent in developing all vegetable 

 life and vegetable form, in effecting all vegetable changes, 

 and in ripening all vegetable produce. All these effects 

 are performed most efficiently, in the case of every plant, 

 at some different temperature or degree of heat ; and he 

 who ascertains most correctly those heats has taken a 

 gigantic step towards excellence as a gardener. An un- 

 congenial heat is as pernicious to vegetables as to 

 animals. Every plant has a particular temperature, 

 without which its functions become more feeble, or cease ; 

 but the majority of them luxuriate most in a climate of 

 which the extreme temperatures do not much exceed 32 

 and 90. No seed will vegetate, no sap will circulate, in 

 a temperature at or below the freezing-point of water. 

 No cultivation will render plants, natives of the torrid 

 zone, capable of bearing the rigours of our winters, 

 although their offspring, raised from seed, may be ren- 

 dered much more hardy than their parents. Others are 

 capable of resisting the greatest known cold to which they 

 can be exposed ; yet all have degrees of temperature 

 most congenial to them, and if subjected to lower 

 temperatures, are less or more injured proportionately 

 to the intensity of that reduction. If the reduction of 

 temperature be only slightly below that which is con- 

 genial, it merely causes the growth of the plant to 

 diminish and its colour to become more pale ; this effect 

 being now produced by the plant's torpidity, or want of 

 excitement to perform the requisite elaboration of the 

 sap, as it is by over-excitement when made to vegetate 

 in a temperature which is too elevated. 



If blossoms are produced at all, they are unfertile, 

 and the entire aspect of the plant betrays that its secre- 

 tions are not healthy, and its functions are deadened. 

 Mr. Knight says, " That melons and cucumber plants, if 

 grown in a temperature too low, produce an excess of 

 female blossoms ; but if the temperature be too high, 

 blossoms of the opposite sex are by far too profuse." 

 The drier the air the greater is the amount of moisture 

 transpired ; and this becomes so excessive, if it be also 

 promoted by a high temperature, that plants in hothouses, 

 where it has occurred often, dry up as if burned. The 

 justly lamented Mr. Daniell has well illustrated this by 

 showing, that if the temperature of a hothouse be raised 

 only five degrees, viz. from 75 to 80, whilst the air 

 within it retains the same degree of moisture, a plant 

 that in the lower temperature exhaled fifty-seven grains 

 of moisture, would, in the higher temperature, exhale 

 one hundred and twenty grains in the same space of time. 



Plants, however, like animals, can bear a higher 

 temperature in dry air than they can in air charged with 

 vapour. Animals are scalded hi the latter if the tempera- 

 ture is very elevated, and plante die under similar cir- 

 cumstances, as if boiled. MM. Edwards and Colin found 

 kidney-beans sustained no injury, when the air was dry, 

 at a temperature of 170 ; but they died in a few minutes 

 if the air was moist. Other plants under similar circum- 

 stances would perish probably at a much lower tempera- 

 ture ; and the fact affords a warning to the gardener 

 to have the atmosphere in his stoves very dry whenever 

 he wishes to elevate their temperature for the destruction 

 of insects or other purposes. 



