RKJUVENESCENCE IN NATURE. 135 



cells originating in this way are ordinarily shorter than 

 those of the earlier generations, and enter into conju- 

 gation* in the well-known way, subject to many 

 modifications. Through the union of the contents of the 

 two conjugated cells, is formed, either in one of the two 

 cells, or in the link connecting them, a globular or longish 

 smooth spore, clothed with a multiple coat, from which 

 the young plant is developed after a long stage of rest. 

 In Spirogyra the coats of the seed-cell (spore) are thus 

 torn, — first the outer, thinner, water-clear coat, next the 

 inner, thicker, yellowish spore-coat is stripped off, and 

 the contents, transformed into the germ-cell and clothed 

 with a new coat, emerge in the form of a spindle-shaped 

 body, having both ends of like character,! which bears 

 great resemblance to the solitarily living cells of the 

 Desmidiaceous genus Spirotcenia.X But the observations 

 of Thwaites, who saw the contents of the ripe spore 

 separate into four portions in certain Zygnemacese, par- 

 ticularly Mesocarpus and 8taurocarpus,% testify that a 

 formation of several germ-cells or young plants in one 

 spore may occur in this family. 



Essentially different from the conditions of the 

 Desmidiacese and Zygnemacese is the propagation of 

 Palmoglaa, a genus which has hitherto been reckoned 

 among the PalmellaceEe, to which, although the occur- 

 rence of a conjugation of the cells might incline one to the 

 opposite view, it is certainly more intimately related 



liave not been able to follow the observation of the germinating plant as far 

 as the commencement of root-formation. (See Pringsheim, on Spirogyra, 

 ' Mora/ 1853 ; Transl. in 'Annals of Nat. Hist.,' 2d ser., vol. xi, 310.— A. fl.) 



* Vide Hassall, 'British Fresh-water Algse,' (1815) t. xviii — xUx. 



I The germination of the Spiroffyrcs was observed by Vaucher (' Hist, 

 des Conferves d'eau douce,' 1803). 1 have seen it take place in the above- 

 described way in July of the present year, in Spirogyra retiformis, which had 

 been collected with ripe spores eleven months previously. I shall mention, 

 hereafter some of the remarkable changes in the contents of the spores 

 occurring as preparatory to germination. (See Pringsheim, L c. — A. H.) 



% Vide Ralfs, 1. c, t. xxxiv, f. 1, 2. 



§ I am only acquainted with these observations from- the report in the 

 ' Botanisohe Zeitung,' 1816, p. 198. ('Ann. Nat. Hist.,' xvii, 203. See on 

 this subject also Pringsheim on Spirogyra, 1. u., p. 296. — A. H.) 



