186 



or varieties, distinguished by specific names in England, to a few 

 typical species ; and that he suggests also the likelihood of two or 

 three additional species for our Flora." 



Under the head ' Literature ' the following works are noticed : — 



* Researches on the Sleep of Plants. By M. Hoffmann, Prof of 

 Botany in Giessen. Heinemann, Giessen, 1851. 8vo, pp. 29.' 



' Pocket Flora of Jena. By C. Bogenhard ; with an Introduction 

 by Prof Schleiden. Leipsic, Engelmann, 1850. 12mo, 483 pages.' 



The following paragraphs, from the brief notice of the first little 

 brochure, are interesting : — 



" The author runs through the different causes to which the phae- 

 nomena known under the name of the sleep of plants can be attributed, 

 in particular, conditions of moisture, electricity, light, expansion of 

 gases within the substance of plants, heat, &c. ; and through a series 

 of interesting experiments, here described, he arrives at the conclu- 

 sion that heat is the cause both of the awakening and the sleeping of 

 plants, and that light only enters into those effects insofar as it con- 

 tains heating rays. Plants, especially their leaves and flowers, unfold 

 after the receipt of a certain sum of degrees of temperature, and are 

 thus far, leaving out of view the chemical influence of light, indirectly 

 dependent upon the sun, which is the sole source of the heat." 



" Pemnanent heat causes a condition of contraction ; a very great 

 depression of temperature passing over during the perfect expansion 

 acts in like manner, yet with essential differences, so that the plant is 

 not exhausted by it, but on the return of warmth exhibits a new and 

 perfect expansion. The condition occurs in extreme frequency in 

 wild vegetation, and at every considerable sudden change of weather. 

 A sudden but transient increase of temperature acts in the same way. 

 With regard to the internal conditions producing these movements, 

 the author attempted to find an explanation by placing thin slices of 

 the pulvinus of the leaves of Mimosa and Oxalis in water, between 

 plates of glass, and examining the relative positions of the elementary 

 organs under the microscope, next quickly heating the fluid between 

 the glass plates over a spirit-lamp, and then comparing anew the re- 

 lative position of the parts under the microscope. He believes that 

 he observed a contraction, by heat, of the exposed and somewhat un- 

 rolled spirals, which might well cause an alteration in the length of 

 the parts." 



The 'Pocket Flora of Jena' is spoken of with commendation. 



A list of the contents of the following journals is given : — ' Annals 

 of Natural History,' Hooker's ' Journal of Botany,' ' The Phytologist,' 

 Schlechtendal's ' Linnaia.' 



