182 M. Berghaus on the Epochs of Vegetation. 



increase of light, be about the same as that occupied in taking 

 landscapes or other distant objects. The Parisians will, of 

 course, have the same advantage over us in taking portraits 

 as in taking other objects, in consequence of their greater in- 

 tensity of light. 



These are the results of my experiments in Daguerreotype, 

 which I have stated as briefly as possible, that I might not 

 take up too much of the valuable time of this Society. 



On the Epochs of Vegetation. By M. Henry Berghaus of 

 Berlin. 



Nature has made essential distinctions in the period of ger- 

 mination, which, as is well known, are in a great measure 

 caused by the constitution of the seeds themselves. Thus 

 rye, millet, and most of the cerealia, germinate in two or three 

 days ; lettuce, the gourd, and the water-cress, in from five to 

 seven ; the bean and onion in about twenty ; parsley in forty 

 days ; columbine, the almond, the chestnut, the peony, the 

 hazel-nut, &c. in from six to eight months ; and, finally, the 

 rose germinates between the first and second year. 



As caloric is the most powerful of the agents which ope- 

 rate on vegetation, so must it also exercise the greatest and 

 most direct influence on germination. Consequently the prin- 

 ciple may be adopted that this phenomenon of vegetable growth 

 stands constantly in connection with the different degrees of 

 temperature of the soil by which the seeds are surrounded. 



We recognise a more evident proof of the truth of this prin- 

 ciple in the fact that the seeds of tropical plants, when sown 

 in temperate climates, germinate much later than in their 

 ■native soils ; while the germination of seeds of colder coun- 

 tries is extraordinarily hastened by their being sown in tem- 

 perate climates. 



Hence, in the greenhouses of our botanic gardens, we must 

 elevate the temperature considerably in order to induce ger- 

 mination in the seeds of tropical countries ; and hence we 

 must shelter the seeds of northern countries in the coldest and 

 most shady spots in order to hasten their vegetation. 



The difference of temperature, likewise, which occasionally 



