WHITE RUSTS. 127 



in further 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 opening, whence they have 

 been expelled, in a globular mass. Soon, however, 

 they begin to move, vibratile cilias 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 



