SELECTED NOTES, ETC. 189 



the mycelium shape themselves into oogonia, in each of which an 

 oosphere is formed out of a portion of the protoplasm. From 

 another branch of the mycelium, a branchlet grows towards the 

 oogonium, swells, and becomes closely attached to it ; and the 

 thicker part becoming separated by a septum (just as takes place 

 with the oogonium itself), developes into an antheridium. As 

 soon as the oosphere is formed, a fine branch of the antheridium 

 reaches it, penetrating the membrane of the oogonium. After 

 fertilisation, the oosphere becomes surrounded by a coat, which 

 thickens and forms a rough, dark-brown external covering, or exo- 

 spore, and an inner endospore. These oospores, which remain 

 dormant throughout the winter and then germinate, are the so- 

 called " resting-spores," and a curious point in connection with 

 this is that the resting spore in some cases attains its full devel- 

 opment on a host other than the one on which it is usually found. 

 Thus, the resting-spore of the lettuce Peronospora is more fre- 

 quently found on common groundsel, or on sow-thistles, than on 

 the lettuce; and De Bary suggests that some member of the 

 order Scrophidariacece may yet turn out to be a commoner host for 

 the resting-spores of the potato fungus than the potato plant 

 itself. De Bary also suggests that in some cases where the rest- 

 ing-spores are not found, the mycelium of the fungus may become 

 perennial, and thus carry the fungus over the winter by discharging 

 the function of hibernation. 



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Argulus foliaceus from Stickle-back and other fishes, are not 

 difficult to obtain, as . the Stickle-backs found in clayey pools 

 generally possess several. They should be lifted off the fish with 

 a knife, and dropped at once into the mounting medium. Glycerine- 

 jelly, or Dean's gelatine, is preferable to balsam for such delicate 



