ON THE NATURAL SYSTEM IN BOTANY. 155 



in the most rigorous period of winter. Sometimes, all circumstances 

 being apparently equal, the phosphorescence is considerable during 

 one night and scarcely visible the night following. Does the atmos- 

 phere favour the escape of light, or this combustion of phosphoric 

 hydrogen? or do these differences depend on chance, which conducts 

 the navigator into a sea more or less rilled with the gelatine of 

 mollusca ? Perhaps these shining animalcules come to the surface of 

 the sea only when the atmosphere is in a certain state. M. Bory 

 St. Vincent asks, with apparent reason, why our swampy fresh waters, 

 filled with polypi, are not luminous ? It would seem that a peculiar 

 mixture of organic particles is necessary to favour the production 

 of light ; the wood of the willow is more frequently phosphorescent 

 than that of the oak. In England, they have succeeded in rendering 

 salted water luminous, by throwing into it the brine of herrings. 

 On most other points, galvanic experiments prove, that the luminous 

 state of living animals depends on the irritation of the nerves. I 

 have seen a dying fire-fly (Elator noctilucus) emit a strong light when 

 I touched its anterior extremities with pewter or silver. 



DR. G. JOHNSTON ON THE NATURAL SYSTEM IN BOTANY*. 



ALL genuine field observers must be familiar with the name of Dr. 

 George Johnston ; for though we are not aware that he has published 

 any separate work, besides the one now before us, he has contributed 

 a considerable number of detached papers to various scientific perio- 

 dicals, all characterised by accurate and acute personal observation, 

 by a fine vein of excursive and tasteful literary illustration, and, 

 what is still better, by sterling common sense, founded on induction, 

 and uncontaminated by fashionable discipleship to schools and sys- 

 tems. In these respects, the Doctor seems to us to stand unique and 

 alone among our British naturalists, as well as in his peculiar attention 

 to neglected branches of his favourite science, neglected, from the 

 subjects being usually unobtrusive ; and on this account it may not be 

 improbable that they attracted his notice, as being in unison to his 

 own retiring and unobtrusive character, which all who know him must 



* Flora of Berwick-upon-Twoed, Vol. II. Cryptogamous Plants. By George 

 Johnston, M. D M &c. 12mo. Edinburgh. 



