REJUVENESCENCE IN NATURE. 193 



The contents of these cells mostly exhibit an abundant 

 formation of oil, of which scarcely any perceptible trace 

 otherwise occurs, and they decay finally with various 

 phenomena of dissolution ; but the cell-membrane is still 

 firm and uninjured after the death'of the contents. All 

 this proves beyond doubt the relation of the softening and 

 solution of the membrane to the -processes of Rejuve- 

 nescence in the contents of the cell. A similar softening 

 and solution of the cell-membrane occurs in Botrydium* 

 at the period of formation of the germ-cells. The vesicle, 

 of a leek-green colour at the time of the vegetative com- 

 pletion, assumes a sea-green colour at the period of 

 ripening, which results from the thickening and clouding 

 of the cell-membrane which occurs at this time; the 

 previously indistinguishable laminated structure of the 

 membrane becomes clearly visible about this time, and 

 the cell-membrane, become limp by softening, collapses, 

 finally melting away, and leaving the germ-cells behind 

 upon the ground. The solution and resorption of the 

 parent-cell membranes, so frequently occurring in the 

 tissues of plants, which have been most accurately observed 

 in the formation of the spores of the Ferns and Mosses,f 

 as also in the formation of the pollen of the Phanerogamia, 

 undoubtedly depend upon similar processes. The gela- 

 tinous thickening of the membrane of the mother-cell 

 mentioned both by Nageli} and Unger, is probably 

 intimately connected with the quickly succeeding re- 

 sorption. 



We may also again call attention here to analogous 

 occurrences in the compound structure of the plant. As 

 the old envelope of the individual cell becomes softened 

 and dissolved, and vanishes imperceptibly, in the trans- 



* Vide supra, p. 128. My observations were made on the smaller 

 species of this genus, B. Wallrothii, Kiitz. 



t For the latest resaaches on this head, see Hofmeister, ' Fruchtbilduug, 

 &c., der holier. Kryptogamen,' 1850. 



% 'Zur Entwicklungs-geschichte des Pollens der Phanerogamen,' 1842. 



' Ueber Merismatiscne Zellbildung bei der Entwicklung des Pollens,' 

 184-1. 



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