EE.TUVENESCENCE IN NATURE. 157 



except at a few points. The soon succeeding collapse 

 and dissolution of the cell is distinctly opposed for some 

 time by a membranous bounding-structure. In very large 

 gonidia, especially those of Vaucheria clavata, this mem- 

 brane exhibits considerable thickness, so as to be clearly 

 distinguishable as such, but in this very case it shows that 

 it possesses totally different properties from those of the 

 cell-membrane subsequently enveloping it : vfhile the 

 cell-membrane, be it ever so delicate, appears tough 

 and extensible, the primordial utricle is found soft and 

 brittle, so that the slightest injury destroys its continuity, 

 which, however, takes place so as to seem rather a 

 separation or flowing apart of the substance than a 

 tearing through.* It is this primordial utricle which 

 bears the numerous vibratile cilia clothing the whole 

 surface of the cell in Vaucheria, these appearing to be 

 formed out of the substance of the coat itself and mere 

 processes of it. Iodine causes these cilia to contract to 

 a certain extent, and acquire a brownish-yellow colour, 

 which colour presents itself the more distinctly, the more 

 abundantly and closely the cilia are collected together, 

 as, after Vaucheria, is the case especially in (Edogoiiium 

 and Bulbocheste, where they form a dense crown of 

 cilia. The body of the germ-cell acquires a deep brown 

 colour with tincture of iodine ; the hyaline apex mostly 

 existing in the stage of motion, as well as the primordial 

 utricle, indistinguishable from the contents in small 

 swarming-cells, have this colour, sometimes appearing a 

 little lighter. This colouring agrees with the well-known 

 behaviour of the primordial utricle of the cells of the 

 Phanerogamia.t The cilia disappear with the com- 

 mencement of the rest, and before the formation of the 

 proper cell-membrane, not only in Vaucheria, but in all 

 Algse where the germ-cells have a ciliary motion of short 



* So says Unger, 'die Pllanze im Momente der Thierwerduiig,' 1845, 

 p. 36. 



t Vide H. von Mohl, 'Botanische Zeitung,' 1844, p. 276. (Transl. in 

 ' Scientiiie Memoirs,' vol. iv, p. 93. — A. H.) 



