Scientific Intelligence — Botany. 191 



BOTANY. 



11. The Effect of very Low Temperature on Vegetation. — In 

 1838, I published, says M. A. de Candolle, in the Bulletin de la 

 Classe d' Agriculture de Geneve (No. 120, p. 171), in an article on 

 the intense cold of January 1838, the following remarks. After first 

 alluding to the observations of Pictet and Maurice, who found the 

 temperature of the centre of a chestnut tree below zero, and also the 

 experiments of M. Ch. Coindet, who after a prolonged cold had ex- 

 tracted from the middle of a large tree small crystals of ice. These 

 trees are however not dead. I have myself, after a cold but little 

 intense, seen crystals of ice in the interior of the buds of several 

 trees which have not suffered from it. Young branches, the buds 

 of many trees, and the leaves of the plants of our country, are in 

 winter often penetrated, beyond doubt, with a cold several degrees 

 below zero (centigrade) ; and although the viscous liquids of the 

 slender tubes congeal with difficulty, it must frequently happen that 

 congelation takes place, without the plant or the organ perishing. 

 Thus cold does not kill vegetation by a mechanical action proceeding 

 from the congelation of the liquid, as some naturalists pretend. "We 

 must recognise rather a physiological action, that the vitality of the 

 tissue is destroyed by a certain degree of cold followed by a certain 

 degree of heat according to the peculiar nature of each plant. The 

 vegetable and animal kingdom, according to this view, will act alike. 

 In the same manner as the gangrene that sets in after the thawing 

 of a frozen part causes the death of an animal tissue, so the change 

 or putrefaction which follows a rapid thawing will be the principal 

 cause of the death of the vegetable tissue. It is well known in prac- 

 tice how to manage the transitions of temperature to preserve the or- 

 gans of vegetables. Since 1838, until my connection with the Academy 

 of Geneva ceased, I stated in my annual lectures that cold may 

 act in two ways on vegetation, either 'physically, by the contraction 

 or congelation of the liquids which often does not kill them ; and 

 physiologically, by an action upon the tissues and upon vegetable life, 

 which the laws of physics do not account for. The most striking 

 example of this last is the immediate death of hothouse plants when 

 exposed to a temperature of -f 1 or + 2° C, which causes no con- 

 gelation. The action of the same degree of temperature is very 

 different on two allied species, and sometimes on two varieties of 

 the same species. 



12. Sleep of Plants in the Arctic Regions. — Mr Seemann, the 

 naturalist of Kellett's Arctic expedition, states a curious fact respecting 

 the condition of the vegetable world during the long day of the Arctic 

 summer. Although the sun never sets whilst it lasts, plants make no 

 mistake about the time when, if it be not night, it ought to be, but 

 regularly as the evening hours approach, and when a midnight sun 

 is several degrees above the horizon, droop their leaves and sleep 

 even as they do at sunset in more favoured climes. " If man," observes 

 Mr Seemann, " should ever reach the pole and be undecided which 



