REJUVENESCENCE IN NATURE. 225 



succeed in finding it, although I frequently met with 

 cells recently divided. Not until I selected the earliest 

 hours of morning for the observation, and at last took 

 the precaution of placing specimens in spirit before sun- 

 rise, so as to be able to examine them at leisure later, 

 was I able to make out completely the process of division 

 of the cells in this genus. I shall describe it in the 

 next section of this treatise. 



All these observations furnish the one common result, 

 that the processes of solution and deformation, the more 

 important as well as the slighter, occur at night, under 

 the influence of determinate degrees of temperature,* 

 while, on the other hand, they confirm the experience 

 that the influence of light awakens the plastic processes', 

 formation of substances as well as production of form, in 

 the plant. f A number of well-known phenomena in 

 the great processes of Rejuvenescence of the Vegetable 

 kingdom have an intimate connection with these facts. It 

 is well known that vegetable life awakening from the 

 winter sleep requires, above all things, warm, dull, and 

 damp days, especially the warm showers of spring, to 

 enable it to dissolve the winter provision of nutriment, 

 on which the influence of light of the increasing days 

 may exercise its newly-shaping force ; equally well-known 

 are the effects of the northern summer, which brings 

 many plants into flower and fruit more rapidly than our 

 temperate climate. It is the influence of light, increased 

 by the long days, which causes a more rapid development 

 of all products of form, an abbreviated course of the 

 metamorphosis, just as we see the plants on high moun- 

 tains also advance with more rapid steps to flower and 

 fruit, through less luxuriant development of the vegetative 



* More exact observations are yet to be made on this point in the Algae. 

 The rapid commencement of the formation of gonidia in Algae brought into 

 the house, doubtless depends on the slighter degree of cooling occurring 

 during the night indoors. 



f See the observations on Euastrum mentioned in the preceding page. 

 I shall describe more minutely, in the Appendix, the important changes of 

 form which the new-born cells of Pediastrum undergo in the course of the 

 first day, and after a nocturnal rest, again on the second day. 



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