132 PRACTICAL BOTANY. 



cells of the plant on which they are parasitic. Some of 

 these plants live, under different conditions, either as para- 

 sites or saprophytes. Some grow in the dead bodies of 

 animals. An alternation of generations occurs, at least 

 in most species. The ordinary form of the plant is the 

 gametophyte. 



Stalks rise from the mycelium of mildews through the 

 stomata, and develop at their ends gonidia filled with 

 spores. Late in the season a special kind of gonidium, 

 known as a perithecium, is developed which bears the 

 spores that continue the life of the plant through the 

 winter. The gonidia of the white rusts are developed in 

 chainlike rows just below the epidermis. The oogonia 

 and antheridia of the sexual reproduction are also pro- 

 duced beneath the epidermis in the intercellular spaces of 

 the host plant, on branches of the stalks or hyphse. 



CYSTOPUS CANDID US. PRACTICAL STUDIES. 



Obtain some Shepherd's Purse or some Purslane, and 

 some of the flowers of Radish, affected with Cystopus. 

 Preserve in alcohol. Alcoholic material may be used for 

 all the observations except Number 3. 



1. Notice the sori or white spots formed by the Fungus 

 on the leaves. Find some that are beginning to form 

 under the epidermis. As the Fungus develops, the epi- 

 dermis gives way and the Cystopus is exposed to the air. 

 Shake a matured and dry specimen over a dark surface, 

 and some of the asexual spores will fall out. 



2. With the forceps tear off some of the white growth 

 and mount in water. Examine with high power. Numer- 

 ous ovoid asexual spores of Cystopus will be found. If 

 the specimen was not too dry, some will be found still con- 

 nected in short chains. Do you find chlorophyl bodies? 

 Test for starch. Is it present ? 



