REJUVENESCENCE IN NATURE. 203 



have not succeeded in seeing in its stage of transition, 

 must doubtless depend upon a complete internal disso- 

 lution of the contents of the seed-cell by transformation 

 of the fixed oil, preceding the division and external 

 assumption of new shape. Since Palmoglma does not 

 grow in water, but on damp rocks and moss, and in its 

 formation of seed coincides with the commencement of 

 the warm and dry season of the year, it is probable that 

 the gradual transformation of the oil begins even in the 

 period of dryness, even requires the drying up as a con- 

 dition of this process. That which I can only express as 

 a conjecture in regard to Palmoglma, is a certainty in the 

 following examples. Fenium curtmn* is a small Desmi- 

 diaceous plant allied to Closterium, growing in rain pools, 

 which are alternately quickly filled and dried up in the 

 changes of weather. In late autumn and in spring many 

 pools in the neighbourhood of Freiburg appear filled 

 with bright green clouds, which are formed by the social 

 growth, and the very fluid, widely extended gelatinous in- 

 vestment of the cells. The gradual ascent of these delicate 

 green clouds from the muddy bottom, when the little 

 basins of water fill again after a dry period, presents a 



* See above, p. 181. Ralfs ('British Desmid.,' p. 109) included this 

 little plant, discovered by Br^bisson, first placed under Closterium and then 

 separated from it in the genus Penium, among the Euastra, and in the 

 genus Cosmarium, a mistake from which a more thorough regard to the 

 arrangement of the cell-contents would have saved hira. According to 

 Nageu, Penium ciertum should be referred to the genus Lysphinctium, sub- 

 genus Adinotcenium ; it is very like the T). Regellanum figured by him, 

 ('Einz. Alg.,' 109, t. vi, e), but. differs in Ihe more numerous green longi- 

 tudinal bands. The plant here named is also remarkable for exhibiting the 

 peculiar movement of the Desmidiaoeae more regularly and more actively 

 than the other members of the family, a motion very different from that of 

 the DiatomacesE. It is a remarkable si^ht to behold all the individuals in a 

 dish of water in a short time turn their long axes toward the light, and 

 thus arrange themselves in beautiful stress in the gelatinous mass. 

 Observation with the microscope shows that it is the younger half of the 

 cell, distinguishable as such for a long time after division, which here 

 turns toward the light. For those who believe in the animal nature of the 

 Desmidiaceae, I will add, that the cell-membrane of Penium is totally 

 destroyed by a red heat, so that it is not a siliceous lorica ; on the other 

 hand, it remains uninjured when boiled in solution of potash. 



