1910-11.] Mathematical Theory of Random Migration. 
287 
Apargia hispida. 
In the Belvidere Hospital there are long straight terraces adjacent 
to the Clyde constructed as in the diagram (Diagram IX.). It is the 
custom to mow the level parts of the terraces with a lawn mower. 
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No plant, therefore, of any high habit can ever seed there. It can 
only grow herbaceously. On the bank between the terraces, however, 
such plants can develop, and a considerable stretch of the bank is 
thickly overgrown with Apargia. The seeds of this scatter over the 
lower and higher terraces, when they germinate and form plants in 
the grass. 
This case can easily be considered as one where there is an infinite 
