THE BEGINNINGS OF II FE. 419 



green colour (f, b.) These filaments sometimes appear 

 to spring at once from the outer layer of the filament, 

 and sometimes from an expanded base, also having 

 a greenish colour, which soon becomes surrounded by 

 a dark brown decolourized zone (^, e'.) The zone 

 often persists long after the Desmid itself has dis- 

 appeared. At other times I have seen attached to the 

 same kind of base (on specimens of Cladophora) a large 

 ovoidal and perfectly hyaline envelope containing in its 

 centre an aggregation of bright green algoid spherules 

 {a\ each of which seems to be capable of enlarging and 

 transforming itself into an Astasia. Diatoms also ap- 

 pear to grow from the surface of the filamentous Alg-ae, 

 to which they are afterwards seen to be attached by a 

 hyaline tubular pedicle j and it is this mode of origin, 

 apparently, to which Dr. Gros referred when he said ' :, 

 'C'est une chose soupgonnte sinon reconnue par tous 

 les observateurs que des vesicules vertes se font jour a 

 travers le tube des Conferves, et se convertissent en 

 Navicules.' Although many Algx present phenomena 

 of this kind, in none are they more striking than in 

 certain specimens of Vaucheria. Filaments of this 

 weed which but a few days before — when placed for 

 observation in a watch-glass — may have showed neither 

 Diatoms nor Desmids upon their surface will at times 

 become crowded, both inside and out, with a rich va- 

 riety of both of these modes of growth. And although 

 it is quite possible that in all such instances the 

 ^ Loc. cit., p. 316. 

 E e ^ 



