FROG-HOPPERS. 



FROST. 



sensible frog. The sensible frog occupies the 

 whole of the back part of the foot, above the 

 horny frog and between the cartilages. See 

 SHOKINS. 



FROG-HOPPERS. The familiar name ap- 

 plied to singular insects (Cercopidida), \vhich 

 pass their whole lives on plants, upon the 

 stems of which the eggs are deposited in au- 

 tumn. " The following summer they are hatched, 

 and the you,ng immediately perforate the bark 

 with their beaks, and begin to imbibe the sap. 

 They take in such quantities of this, that it 

 oozes out of their bodies continually, in the 

 form of little bubbles, which soon completely 

 cover up the insects. They thus remain en- 

 tirely buried and concealed in large masses 

 of foam, until they have completed their final 

 transformation, on which account the names 

 of cuckoo-spittle, frog-spittle, and frog-hoppers 

 have been applied to them. We have," says 

 Dr. Harris, " several species of these frog-hop- 

 pers in Massachusetts, and the spittle, with 

 which they are sheltered from the sun and air, 

 may be seen in great abundance, during the 

 summer, on the stems of our alders and wil- 

 lows. In the perfect state they are not thus 

 protected, but are found on the plants, in the 

 latter part of summer, fully grown and prepar- 

 ing to lay their eggs. In this state they pos- 

 sess the power of leaping in a still more re- 

 markable degree than the tree-hoppers; and, 

 for this purpose, the tips of their hind shanks 

 are surrounded with little spines, and the first 

 two joints of their feet have a similar coronet 

 of spines at their extremities. Their thorax 

 narrows a little behind, and projects somewhat 

 between the bases of the wing-covers ; their 

 bodies are rather short, and their wing-covers 

 are almost horizontal and quite broad across 

 the middle, which, with the shortness of their 

 legs, gives them a squat appearance." 



FROGS (Rana, Linn.). A genus of amphi- 

 bious reptiles, consisting of 17 species, but two 

 only require to be here noticed: 



1. The Common Frog (A\ teuton-aria), which 

 is too well known to need description. Some 

 of its properties are very singular, particularly 

 its powers of leaping and swimming. Its body 

 is naked, and without any tail ; the fore limbs 

 are very lightly made, while the hind legs and 

 thighs are remarkably long, and furnished with 

 strong muscles. As soon as the spawn is vi- 

 vified, the future frog becomes a tadpole, in 

 which state it is wholly a water animal, breath- 

 ing by bronchia or gills, like fish ; but as soon 

 as it is changed into a frog, and attains its 

 proper shape, it acquires lungs, by which it 

 breathes, and then immediately migrates to the 

 shore. 



2. The Gibbous, Green, or Edible frog (R. 

 esculentu), which differs from the former spe- 

 cies only in having a high protuberance in the 



frogs retaliate by feeding on the spawn and 

 young fry of fish in ponds and rivers. 



Of the utility of frogs, in destroying insects 

 injurious to gardens and farms, the following 

 view presented in a French periodical, is highly 

 favourable to those much despised animals. 



" Gardeners wage the same war against frogs 

 as with moles and all other insects mischievous 

 to their crops. But they are wrong in including 

 frogs in the general proscription, since they 

 not only do them no injury, but render them, 

 on the contrary, important services ; for they 

 are carnivorous as well as herbivorous, and 

 greatly prefer insects to vegetable food. They 

 are particularly fond of snails, and swallow 

 them even with their shells on, when they are 

 not too large. If you open a frog, you will find 

 his stomach full of insects hurtful to agricul- 

 ture, and especially snails. The shells they 

 digest, or rather dissolve in their stomachs, in, 

 the same way that dogs do bones, and turkeys 

 the shells of nuts." (American Farmer.) 



FROND. A combination of stem and leaf 

 in one organ, as in ferns, MarchatUia, and such 

 like plants. 



FROST. In meteorology is the cause of the 

 congelation of water or the vapours of the at- 

 mosphere. Water begins to freeze when the 

 temperature of the air is such that Fahrenheit's 

 thermometer stands at 32. At this tempera- 

 ture ice begins to appear, unless some circum- 

 stance, for example, the agitation of the water, 

 prevents its formation. As the cold increases 

 the frost becomes more intense, and liquids 

 which resist the degree of cold required to con- 

 geal water at length pass into the solid state. 

 When water remains at complete rest it may 

 be cooled down to 28 Fahrenheit without 

 freezing; but the moment it is agitated, the 

 thermometer rises to 32 and the water freezes. 

 In this case the insensible heat of the water is 

 retained when the fluid is at rest. No experi- 

 ments have hitherto ascertained to what depth 

 frost will extend, either in earth or water, but 

 its effects will of course vary according to the 

 degree of coldness in the air, the longer or 

 shorter duration of the frost, the texture of the 

 earth, the nature of the fluids with which the 

 ground is impregnated, &c. In England the 

 frost rarely extends in the ground below 18 

 inches from the surface. Frost is peculiarly 

 destructive to vegetation. During severe frost 

 almost all vegetables fall into a state of decay, 

 and even a moderate degree of frost is suffi- 

 cient to destroy many of the more tender kinds. 

 The injury which vegetables sustain from frost 

 is greatest when it is preceded by a thaw or 

 copious rains ; for the plants are then turgid 

 with moisture, which, expanding in bulk as it 

 passes into the solid state, produces the rup- 

 ture of the vegetable fibres. Therefore it is 

 that a sharp, north wind, or any thing which 

 dries the sap or juices of vegetables previous 

 to frost, tends to their preservation. The great 

 power of frost on vegetables is well known. 

 Trees are sometimes destroyed by it as if by 

 fire, and split with a noise resembling the ex- 

 plosion of artillery, since the juices of the tree 

 expand with great force, as they are converted 

 ( into ice. In winter, however, trees generally 



recommended by Walton as bait for pike, but ' have neither leaves nor flowers, and their buds 



507 



middle 

 angle. 



of the back, which forms an acute 

 Its colours likewise are more vivid, 

 and its marks more distinct, the ground colour 

 being a pale or yellowish green, marked with 

 rows of black spots from the head to the rump. 

 The flesh of the hind thighs is used as a re- 

 storative food. The flesh of the Surinam frog 

 (R. paradoxa) is also used as food. Frogs are 



