HYDROCLEIS 



444 



HYGROMETER 



leaves, floating on ponds and still waters. Runners. 

 Soil unnecessary. 



H. Mo'rsus-Ra'nce (Frog-bit). J. White. England and 

 Ireland. 



HYDRO'CLEIS. (From hudor, water, and kleis, a bar ; 

 from the obstruction to the water in rivers and lagoons. 

 Nat. ord. Alismaceae.) 



Stove perennial aquatic. Divisions ; runners ; seeds. 

 Loam in tubs or the shallow part of a tank. 

 H. Commerso'ni (Cpmmerson's). i-ij. Yellow. May 



to July. Brazil. 1831. 



HYDROCO'TYLE. Pennywort. (From hudor, water, 

 and kotule, a hollow ; in allusion to the little hollow in 

 the centre of the round leaf. Nat. ord. Umbelliferae.) 



Dwarf perennial herbs for the bog garden, with in- 

 significant flowers, but more interesting leaves. Seeds, 

 divisions. Any damp soil. 

 H. america'na (American). \. N. Amer. 

 asia'iica (Asiatic), i. Pale pink. Tropical and sub- 

 tropical regions. 



tnoscha'ta (musky). . New Zealand. 

 repa'nda (scolloped). J. N. Amer. 

 rotundifo'lia (round- leaved). J. Asia and Trop. 



Africa. 



umbella'ta (umbelled). \, Trop. regions. 

 vulga'ris (common). jV. Green. Britain. 



HYDROGLO'SSUM SCANDENS FULCHERI. See 



LYGODIUM SCANDENS FULCHERI. 



HYDRO LEA. (From hudor, water, and elaia, oil; 

 referring to the marshy habitat and oily feel of the 

 leaves. Nat. ord. Hydrophylls [Hydrophyllaceas]. Linn. 

 5-Pentandria, z-Digynia.) 



Greenhouse herbaceous plants. Divisions, cuttings, 

 and seeds ; spino'sa is a small aquatic, growing best in 

 peat and loam ; quadriva'lvis is also found in boggy places. 

 H, carolinia'na (Carolinian). Pale blue. July. N. Amer. 



1824. 



,, quadriva'lvis (four-divided). See H. CAROLINIANA. 

 ,, spino'sa (thorny), i. Blue. S. Amer. 1791. 



HYDROME STUS. (From hudor, water, and mestos, 

 half; referring to the plant living in water during the 

 rainy season. Nat. ord. Acanthads [Acanthacea?]. Linn. 

 14'Didynamia, z-Angiospermia. Now referred to Aphe- 

 landra.) 

 H. macula'tus (spotted). See APHELANDRA HYDRO- 



MESTUS. 



HYDROPE'LTIS. (From hudor, water, and pelte, a 

 shield ; referring to the floating shield-like leaves. Nat. 

 ord. W ater shields [Nymphaeaceae]. Linn. i^-Polyandria, 

 6-Polygynia. Now referred to Brasenia.) 

 H. purpu'rea (purple) See BRASENIA SCHREBERI. 



HYDROPHY'LLUM. Water-leaf. (From hudor, water, 

 and phullon, a leaf. Nat. ord. Hydrophylls [Hydro- 

 phyllaceae]. Linn. ^-Pentandria, i-Monogynia. Allied 

 to Nemophila.) 



Hardy herbaceous perennials, from North America. 

 Divisions and suckers ; rich loam and peat ; in marshy 

 situations. 

 H. appendicula'tum (appendaged-ca/y*^). f. Blue. 



May. 1812. 



canade'nse (Canadian). $. White. May. 1759. 

 magella'nicum (Magellan). i. Pink. June, July. 



Magellan region. 1817. 



virgi'nicum (Virginian). . Blue. June. 1739. 

 " Shawanese Salad." 



HYDRO SMB. (From hudor, water, and osme, smell ; 

 in allusion to the peculiar smell of the flower. Nat. ord. 

 Araceas. Now referred to Amprphophallus.) 



Stove Aroids. Offsets and division of tubers. Sandy 

 loam and peat or leaf-mould. 



H. leopoldia'na (Leopoldian). Spathe velvety purple- 

 brown. Congo. 1887. 

 ,, Teu'szii (Teusz's). See AMORPHOPHALLUS EICHLERI. 



HYDROTffi'NIA. (From hudor, water, and iainia, a 

 band ; referring to a triangular band in the flower 

 secreting a liquid. Nat. ord. Irids [Iridaceae]. Linn. 

 S'Triandria, i-Monogynia. Allied to Beatonia.) 



Pretty half-hardy bulbs, with the aspect of a Tigridia, 



and flowers like a Fritillaria. Seeds, sown when ripe, 

 or kept, and given a little heat in the spring ; division 

 of the offsets ; light, rich, sandy loam ; taken up, and 

 kept after the foliage is decayed, and planted out the 

 following spring. If left in the ground, and covered to 

 protect from rains and frosts, the plants will be stronger 

 than if the bulbs were kept dry all the winter. 

 H. loba'ta (lobed-flowered) . ij. Yellow, purple. May. 

 Lima. 1843. 



Melea'gris (Guinea-fowl-like), i. Yellow. July. 

 Mexico. 1837. 



Kart//ow'*tei(VanHoutte's). Mexico. 



HYGROMETER. An instrument for ascertaining the 

 quantity of moisture in the air. Everything that swells 

 by moisture, and contracts by dryness, is capable of 

 being formed into one. Every gardener who has taken 

 a cool bunch of grapes into a hothouse well-supplied with 

 moisture would, in the grapes almost instantly being 

 covered with dew, see the principle upon which the 

 hygrometer acts. The colder the grapes, the warmer 

 the house, the more the vapour contained in it, the 

 sooner would the dew be formed, and the more plentiful 

 its depositure. Pouring cold water into a glass tumbler, 

 in similar circumstances, will be attended with a similar 

 result : dew will be deposited on the outside of the glass ; 

 because, in either case, the cold body condenses the 

 vapour in its neighbourhood ; and this is what is called 

 the dew-point, being that temperature at which moisture 

 is deposited from the surrounding atmosphere upon any 

 object of that particular temperature. The drip in 

 frames, greenhouses, &c., is similarly caused. The 

 thermometer is the best instrument for showing the 

 temperature ; and by taking two similar ones, covering 

 their bulbs with a fold of muslin or silk, keeping one dry 

 and the other wet, with a thread of floss-silk acting as a 

 syphon from a vessel of water, the greater the difference 

 of temperature indicated by the moist and dry ther- 

 mometer, the greater the deficiency of atmospheric 

 moisture. The nearer the temperature of the moist and 

 dry bulb, the nearer is the air to being saturated with 

 moisture. To obtain more perfect details Daniel's Hygro- 

 meter may be used. It consists of two hollow glass balls 

 containing ether, and communicating by the glass tube 

 which rests on the support. The ball which forms the 

 termination of the longer leg is of black glass, in order 

 that the formation of dew on its surface may be the 

 more perceptible. It includes the bulb of a delicate 

 thermometer dipping in the ether, its scale being inclosed 

 in the tube above the ball ; and whatever change takes 

 place in the temperature of the ether is indicated by this 

 thermometer. The other ball is covered with muslin. 

 In making an observation it is first necessary to note 

 down the temperature of the air ; next turn the instru- 

 ment, so that when the muslin- covered ball is held in 

 the hand, the ether may escape into the blackened ball ; 

 and it should also be held till the included thermometer 

 rises a few degrees above the temperature of the air, 

 when it should be replaced on the support. Then drop, 

 or gently pour, a little ether on the muslin. The evapora- 

 tion of this extremely volatile substance produces cold ; 

 and attention must be instantly directed to the black 

 glass ball and included thermometer. The latter will be 

 seen falling rapidly ; and at length a ring of dew will 

 appear at the line which runs across the black ball 

 quickly, if the air is very moist, slowly, if the air is dry. 

 If the air is very dry, no moisture will be thus deposited 

 till the thermometer falls to 10, 20, or 30 below the 

 temperature of the air. But at whatever temperature 

 the dew forms, that temperature should be noted as 

 the dew-point ; and the difference between it and the 

 temperature of the air, at the time, is the degree of dryness 

 according to the indications of this hygrometer. Thus, 

 in a moderately dry day, let it be supposed that the 

 temperature of the air is 65 in the shade, and that the 

 muslin requires to be kept moist, before dew is formed, 

 till the blackened ball containing the ether has its 

 temperature reduced to 50, as indicated by the included 

 thermometer ; there are then said to be 15 of dryness. 

 Again, supposing the temperature is 85, and the dew- 

 point found, as before, to be 70, the degree of dryness is 

 still expressed by 15 ; but the quantity of moisture 

 diffused in the air is, notwithstanding, somewhat greater 

 in the latter case than in the former. If 1000 represent 

 complete saturation, the quantity of moisture, when the 



