WHITE RUSTS. 127 



in furtlier confirmation. If the conidia (white 

 spherical bodies ejected from the pustules of the 

 ^'' white rust^'') are sown in a drop of water on a 

 glass slide^ being careful to immerse them entirely^ 

 they will rapidly absorb the water and swell ; soon 

 afterwards a large and obtuse papilla^ resembling 

 the neck of a bottle^ is produced at one of the 

 extremities. At first vacuoles are formed in the 

 contents of each conidium ; as these disappear^ the 

 whole protoplasm (granular substance filling the 

 conidium) becomes separated by very fine lines 

 of demarcation^ into from five to eight polyhedric 

 portions^ each with a faintly coloured vacuole in 

 the centre. These portions are so many zoospores. 

 Some minutes after the internal division^ the papilla 

 swells and makes itself an opening_, through which 

 the zoospores are expelled one by one^ without 

 giving any signs of movement of their own. They 

 take a flat disk-like or lenticular form^ and group 

 themselves about the openings whence they have 

 been expelled^ in a globular mass. Soon_, however^, 

 they begin to move^ vibratile ciliae show themselves_, 

 and by means of these appendages the entire 

 globule oscillates^ the zoospores disengage them- 

 selves from each other^ the mass is broken up_, 

 and each zoospore swims off on its own account 

 (plate X. fig. 208). 



The free zoospores are of the form of a plano- 

 convex lens^ obtuse at the edge. Beneath the 

 plane face^ out of the centre^ and towards that 



