RKJUVENESCENCE IN NATURE. 205 



up they all clearly run together, and fill the cell in an 

 uniform mass, by which the two starch-grains previously 

 hidden among the crowd of oil-drops, become very dis- 

 tinctly evident. With this condition of formation of oil 

 commences a stage of rest in the life of this httle 

 organism ; the cells no longer increase by division ; the 

 stimulus of light no longer produces any movement ; the 

 gelatinous envelope vanishes without any new formation 

 of jelly. Unless peculiar circumstances arise, the indi- 

 viduals gradually die away, entirely losing their colour. 

 But if the water is allowed to dry up (as happens from 

 time to time in the natural habitations of this plant), and 

 the dried remains are again immersed in water, after a 

 shorter or longer period,* new gelatinous clouds rise up 

 afresh on the following day, in which are found a multi- 

 tude of newj again freshly vegetating individuals, con- 

 taining, instead of the former oil vesicles, homogeneous 

 green contents, in which the green longitudinal bands 

 are again soon to be distinguished. The multiplication 

 by division also soon commences again. That these 

 rejuvenised, revived individuals are not a brood originating 

 from spores, is shown by their size, which agrees with 

 that of the dried-up individuals.! 



I have observed still more completely the Rejuvenes- 

 cence, caused through drying up, in the probably oleiferous 

 cells of the Chlamidococcus pluvialis, already many times 

 referred to.f 



* I have not yet made out how long the life can be retained in the dried 

 condition, in Penium curium. 



f I have not unfrequently seen a filling of the old cells with drops of oil, 

 similar to that in Penium curium, in other Desmidiacese, in Diatomaceae, 

 Pediastrum, Conferva hombyeina, and exceptionally, as above mentioned, in 

 Hydrodietyon. In most cases this formation may end with the death of the 

 cell ; this is tolerably certain in Pediastrum particularly. 



X See above, pp. 138, 158, 184, 200. I can only indicate here the most 

 essential elements of the strange history of this creature, embracing a 

 complicated alternation of generations; to trace it completely through 

 all its normal and abnormal complications, would require a separate essay 

 and numerous pictorial illustrations. As the observation of the many 

 interesting phenomena afforded by this plant is by no means difficult, 

 and as it is desirable that these observatious should be repeated by many 



