REJUVENESCENCE IN NATU11K. 213 



and thicker cell-membrane. Probably the return of these 

 to renewed resting vegetation takes place by a passage 

 through the series of active generations. Every shower 

 of rain will wash away these loose ripe cells of the crusts 

 of C/damidococcus ; carried into collections of rain-water 

 they will soon produce the active brood, which, returning 

 to rest after a few active generations, settles on the margins 

 of the little puddles, and then recurs to the resting mode of 

 vegetative multiplication. At least this seems to me the 

 normal cycle of the life of these little amphibious and am- 

 phibolic Algae. What we intended especially to examine in 

 these, is the appearance and disappearance of a probably 

 oily red colouring matter in connection with the conditions 

 of old age and Rejuvenescence of the cells. We found this 

 most abundantly developed in the resting seed-cells, ar- 

 rived at the entire pause of the vegetation, we saw it 

 vanish almost entirely in the active generations suc- 

 ceeding one another in rapid Rejuvenescence, and en- 

 dowed with power of very rapid growth. The red 

 colouring matter seems to play the same part here as we 

 have ascribed to the formation of oil in the instances 

 previously examined. Since the capability of preserving 

 the life in the dried condition, and the necessity of the 

 desiccation as a preparative for future Rejuvenescence, 

 may be supposed to have a similar cause in Chlamidococcu$ 

 and in other minute Algse, it is not improbable that the 

 red colouring matter is, in this case, either itself of oily 

 nature, or occurs in combination with a fixed oil.* The 

 mode of appearance of this in the cells testifies in favour of 

 this assumption to some extent, to some extent, however, 



* Nageli (' Einzell. Algen.,' p. 9), likewise ascribes the red colour occur- 

 ring in many Palmellacese, partly as a normal (Pleurococcusminiatus,Palmella 

 miniata) partly as an abnormal phenomenon (Tachygonlum, Chlorococcus, 

 E/idococcus) to the formation of an orange-coloured oil in the place of the 

 chlorophyll. Probably all these have the power of retaining their life a long 

 time in the dried condition, in Pleurococcus minialus, at least, I am quite 

 certain of it. In the crusts of Protococcus vii-idis, growing on walls, also, 

 the cells of the uppermost layers, most liable, become dried up, often acquire 

 a brownish-red colour, the origin of which is probably to be explained iu the 

 same \vav. 



