VAUCHERIA 221 



observed in specimens grown under favourable conditions in 

 water : a considerable mass of the Alga is to be placed in a 

 porcelain bowl, in water, and exposed in a window : after a few 

 days, numerous small plants of Vaucheria will he found floating 

 on the surface of the water, or disposed along the submerged 

 surface of the bowl : these have resulted from vegetative repro- 

 duction by zoogonidia. In order to see the process observa- 

 tions must be made in the early morning, or else the culture 

 must be kept in the dark till shortly before the observations are 

 to be made. Shortly after dawn (or soon after the specimens 

 have been exposed to light) some filaments may be seen with a 

 lens to have dark-coloured and slightly swollen ends : these are 

 about to form zoogonidia : mount some specimens without a 

 cover-slip, taking care to avoid injuring them ; and examine 

 under a low power : observe 



1. The swollen end of the filament, with dark, densely aggre- 

 gated protoplasm, surrounding a vacuole. 



2. The transverse septum dividing the swollen end from the 

 rest of the filament. 



If such specimens be kept under observation the escape of 

 the zoogonidium may be observed : the following points are to 

 be specially noted 



1. Various changes in the protoplasmic body and vacuole, 

 terminating in the formation of a transparent, and radially 

 striated, outer protoplasmic coat (ectoplasm), which lines the 

 cell-wall, while darker, more granular protoplasm (endoplasm), 

 including the chlorophyll corpuscles, collects towards the centre. 



2. The rupture of the cell-wall by an irregular slit near to the 

 extreme apex of the filament : before the rupture the septum 

 may be seen to present a convex surface to the rest of the 

 filament, indicating greater internal tension in the " zoosporan- 

 gium " : on rupture, this is relieved, and the septum then pro- 

 jects convexly into the cavity of the empty zoosporangium. 



3! The passage of the protoplasmic mass through the opening, 

 by a streaming movement, assisted by more or less marked, 

 screw-like rotation of the whole body : the protoplasm may 

 undergo division at the time of escape, and two zoogonidia may 

 thus be formed. 



