KKJUVENESCENCK IN NATURE. 221 



found in the lowest internodes of the stein of the 

 perennial Cliara ceratop/iylla, formed in the year pre- 

 vious to that in which it was examined, that the cell- 

 membrane, about ^ millim. in total diameter, was 

 composed of two very distinct portions of about equal 

 thickness ; while the thinner cell-membrane of the yonng 

 internodes of the stem exhibited no such sub-division. 

 In each of the two portions I could make out about 10 

 subordinate layers, which, however, were themselves of 

 compound nature. The agreement of the nocturnal pro- 

 cess of respiration of plants with the phenomena of 

 dissolution, through which we have seen the transition 

 to distinctly new formations prepared, is confirmed by 

 the epoch in which the latter usually make their appear- 

 ance. Observation of the Algae has furnished us with 

 most interesting facts in reference to this. Trentepohl* 

 already observed that the expansion of the summits (the 

 preparation for the formation of the germ-cell) in Vaucheria 

 clavata took place especially in the night, and the exit 

 of the active germ-cell on the succeeding morning. 

 Ungerf confirmed this, for he characterises it as a re- 

 markable phenomenon that the unloosing of the gonidia 

 of Vaucheria mostly occurs between eight and nine o'clock 

 in the morning. According to the statements of Thuret j 

 and Fresenius, the same phenomenon is repeated in 

 other Alga?. I have satisfied myself in all the green 

 Alga3 with active gonidia which I have had an oppor- 

 tunity of observing, that the preparation for the formation 

 of gonidia, and particularly the disappearance of the 

 starch-grains mostly connected with this, begins in the 

 night, and in general advances so far in one night, that 

 the formation of the gonidia can be completed and their 

 birth take place on the following morning. I will first 



* According to Meyen, ' Pflanzenphys.,' iii, p. 430. 



f ' Die Pflauze im Momente der Tiiierwerdung/ p. 27. 



% " C'est surtout le matin qu'ou trouve le plus grand uombre de spores 

 des Conferves en mouvement," Thuret, ' Sur les Organes Locomotenrs des 

 Spores des Algues,' ('Ann. des Sc. nat.,' 1S43, p. 268.) 



' Zur Controverse uber die Verwandlung der Infusorien in Algeii,' p. iv. 



