XL] STONEWORTS, AND PEPPERWORTS. 173 



of the spore-case is devoted to the large single spores ; 

 the upper produces the smaller, numerous granules, 

 which ultimately yield spermatozoids, which fertilise 

 the larger spores. This spore-case is represented at 



fig- 133. 



Pilnlaria is more frequent in the south of Britain 

 than Isoetes, but it requires careful searching amongst 

 the sedges to discover it. Both these 

 plants are easily cultivated, Isoetes form- 

 ing a suitable object for the bottom of 

 an aquarium. They belong, as we have 

 stated, to the order Marsileacece, one FIG. i 33 . 

 species of which, M. macropns, affords 

 the fruit called Nardoo, which the Australian abori- 

 gines made up into a coarse kind of bread, and to 

 which a melancholy interest attaches. When the 

 exploring expedition of Messrs. Burke, Wills, and 

 King had crossed the Australian continent from Mel- 

 bourne to the Gulf of Carpentaria, they were reduced 

 to sore straits on the return journey, finally perishing 

 of starvation. This was their last resource, and Mr. 

 King, who survived, brought some of the spores with 

 him to Melbourne : there are specimens at Kew 

 which were raised from these spores. 



