166 BOTANY. 



276. The resting-spores remain in the tissues of the host 

 until the latter decay, which is generally in the spring. 

 Germination then takes place, in some species by the pro- 

 duction of a tube, in others by the division of the proto- 

 plasm into zoospores (Fig. 85, B, G, D), whose subsequent 

 ' development is like that described above in case of the 

 conidia. 



Practical Studies. — (a) Look for Botrydium in damp weatlier in 

 the summer on the hard, smootli ground of unused paths. It often 

 appears on compact soil in greenhouses in the winter. 



(6) Collect a quantity of Green Felt and preserve it in a dish of 

 water. After a few hours a large number of zoospores may be ob- 

 served collected at the edge of the water nearest to the light. 



(c) Examine carefully mounted specimens of the bright green fila- 

 ments, and look for the thickened lateral branches which produce 

 the zoospores. 



(d) Select some of the oldest, yellowish filaments. Mount and 

 examine with a low power for the sexual organs. In collecting 

 specimens for the study of the sexual organs it is necessary always 

 to take those masses which are yellowish and appear to be dying or 

 dead. 



(«) Throw a dead fish into a pool of water in the summer, and ex- 

 amine it after a few days, when it will probably be found covered 

 with a mould-like growth. Remove a few filaments and look for the 

 formation of zoospores. The same Water-mould (Saprolegnia ferax) 

 may often be found upon the bodies of young fishes, especially in 

 fish-hatching houses. 



(/) In the spring the leaves of shepherd's-purse and peppergrass 

 may often be found covered underneath with a white mould-like 

 growth (Peronospora parasitica). Carefully scrape off a little of this 

 growth and mount first in alcohol, afterwards adding a little potassic 

 hydrate. The irregularly branching hyphas will be seen to bear here 

 and there their white, broadly ellipsoidal conidia. Similar studies 

 may be made of the Grape-mildew (Plasmopara viticola) on grape- 

 leaves in autumn, and the Lettuce-mildew (Bremia lactucse) on culti- 

 vated and wild lettuce from spring to autumn. 



{g) Make very thin cross-sections of a leaf affected with a Downy 

 Mildew, when the latter has passed the period of its greatest vegeta- 

 tive activity. Mount in alcohol (to drive out air-bubbles), then add 

 potassic hydrate, and look for • the resting-spores, which iu some 

 species are of a dark brown color. 



