222 PHYSIOLOGICAL BOTANV. PART IT. 



certain plants, as the fly-catching Lychnises (Lychnis 

 nrmeria and others) appear to be composed of a 

 material of the same nature as common birdlime 

 extracted from the bark of the holly. Several kind of 

 leaf-buds, as those of the horse-chestnut, are coated 

 over with a glutinous insoluble excretion apparently 

 intended to secure them from the ill effects of moisture. 



(2 16.) Wax is a very abundant excretion from 

 many plants. It forms a delicate powder on the sur- 

 face of certain fruits, as the substance termed the 

 " bloom " on the plum. It is so plentiful on the sur- 

 face of poplar leaves, that a manufactory was at one 

 time established in Italy for the purpose of procuring 

 it from them as a material for commerce. It is very 

 abundantly furnished by some palms in tropical countries, 

 where it is advantageously employed for economical 

 purposes ; but the Myrica cerifera is the plant which 

 affords it in the greatest abundance. Its fruit is 

 completely enveloped in a coat of wax, and when 

 thrown into boiling water the wax melts and floats to 

 the surface where it is skimmed off. It has a slightly 

 green tinge which can be removed by chlorine, and it 

 may then be formed into candles resembling sper- 

 maceti. This fruit yields about one ninth per cent, of 

 its weight in wax. All the kinds of vegetable wax are 

 closely allied to common bees' wax in several proper- 

 ties, though essentially distinguished from it by others. 



(217.) Radical Excretion*. But of all excretions 

 proceeding from plants, some of the least-known are 

 perhaps the most important in an economical point of 

 view. It was not until very recently that their pro- 

 perties had been made a subject of experimental in- 

 quiry, or even that their existence had been clearly 

 established ; but the partial results hitherto obtained 

 have opened a wide field for speculation. The excre- 

 tions to which we allude are discharged from the 

 root, and may be detected by a very simple experi- 

 ment. If young French beans, for example, be placed 

 in a glass containing distilled water, at the end of 



