ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 919 



to from 20 to 25 per cent, of the total weight of the leaves. The 

 absolute amount of mineral substances in the stem is considerable, 

 but the relative amount is small, not above about 4 per cent, at the 

 time of the death of the plant. The roots contain very little mineral 

 matter, except when the plant has been deprived of inflorescence ; it 

 gradually decreases during the life of the plant. 



Transpiration of Plants in the Tropics.* — V. Marcano finds that, 

 in the tropics, plants evaporate in the night (from 6 p.m. to 6 a.m.) a 

 quantity of water which is distinctly equal to that which they 

 evaporate during the day. During the day this evaporation takes 

 place chiefly between 6 a.m. and noon. The maximum is remarkable 

 for its constancy and extent, being half or even three-quarters of that 

 which is evaporated during the twelve hours of the day ; it generally 

 takes place after 10.15 a.m., and almost always before noon. From the 

 maximal point to 6 p.m. the evaporation is very feeble. The hygro- 

 metric condition of the air does not seem to have any great influence 

 on transpiration. 



Although nocturnal evaporation from leaves has been denied by 

 the gi-eat majority of vegetable physiologists, the proofs now adduced 

 find support in the views of Boussingault, who speaks of hearing 

 water continually dropping from the neighbouring trees, when 

 bivouacking at night in the open air, and explains it by suggesting that 

 transpiration from the green parts of plants has some share in causing' 

 the phenomenon. 



Chemical Phenomena of the Assimilation of Plants.j — Dr. T. L. 

 Phipson details the experiments which lead him to consider that 

 peroxide of hydrogen plays a great and hitherto unsuspected part in 

 the process of assimilation. 



Histo-Chemistry of Plants. J — In an interesting contribution to 

 the " histo-chemistry " of plants A. Eosoll illustrates the light that 

 can be thrown upon vegetable principles by studying them micro- 

 chemically in situ in the plant. 



The first plant mentioned is Helichrysmn bracteatum, the yellow 

 flower-heads of which are well known as a variety of " everlasting 

 flowers." This yellow colour is very persistent ; but when the dried 

 flower-heads are dipped into borax solution to which hydrochloric 

 acid has been added, the involucral leaflets become of a beautiful 

 ruby red colour. Further investigation showed this yellow i)igment 

 to be a hitherto undcscribod quinone-like substance, which Eosoll has 

 named lielichrysin. In the younger leaflets it exists in combination 

 with protoplasm, whilst in the older ones it has its seat in the 

 residual cell-contents, lielichrysin is soluble in water, alcohol, ether 

 and organic acids; insoluble in benzol, chloroform, and carbon 

 bisulphide ; is coloured purple-red by mineral acids and alkalies ; 

 and is precipitated by metallic oxides and their salts as a red-coloured 



* Comptea Renrlus, xHx (1884) pp. 51-3. Of. this Journal, nntc, p. 87. 



t Cliemicul News, 1. (1«8J) p. 37. 



X Monutdbefte, v. p. 91. Cf. Bull. Torrcy Bot. Clul>, xi. (1881) pp. Ol-S. 



