PROTOBASIDIOMYCETES 



401 



been to a very considerable extent discarded by growers who can- 

 not handle the plant so as to prevent rust. On the other hand, 

 varieties like the Enchantress (daybreak pink) and Lawson (pink) 

 have under a variety of conditions demonstrated a high degree of 

 resistance. Nevertheless, the conditions under which the plants 

 are grown affects to a considerable extent the amount of the rust. 

 Of two growers using cuttings from the same stock with different 

 regard for sanitation and different methods of cultivation, the one 

 may find the rust abundant in his houses, and the other may be 

 able to grow plants practically free from it. It is certain that poor 

 ventilation and conditions permitting the deposit or retention of 

 drops of water upon the surfaces of the leaves is more conducive 

 to the spread of the fungus, but its approximate relations to 

 environmental factors have not been determined. 



The fungus. The life history of this fungus is incompletely 

 known. The uredosporic stage is the common method of propaga- 

 tion, but the teleutosporic stage may also be found under the condi- 

 tions of greenhouse or garden. The uredospores are more or less 

 spherical or ellipsoidal in form, ordinarily varying from 24-35x21- 

 26 p. The cell wall is thick and sparsely beset with minute spines. 

 The uredosporic pustules are pulverulent, light chestnut brown in 

 color, and may be found upon leaves or stems. The teleutospores 

 are not dissimilar in form to the uredospores, and are commonly 

 ellipsoidal, varying from 20-35x18-25^. The rather uniformly 

 thickened chestnut brown membrane is marked by minute wart- 

 like markings best seen in the dry condition. The spores possess 

 terminal germ pores marked by a papillate, hyaline covering. The 

 pedicels are short and colorless. The uredospores germinate read- 

 ily in water, and the experiments made by Stewart indicate that 

 they are unusually resistant to many fungicides and toxic agents. 

 A solution of 1-500 copper sulfate was required to give inhibition 

 of germination, and a still stronger solution to entirely prevent 

 germination. On the other hand, potassium sulfide i-iooo pre- 

 vented germination, and even weaker solutions inhibited consider- 

 ably this process. 



It would appear that the mycelium is not greatly localized 

 in the host, but no accurate determination of this point can be 

 cited. Furthermore, few inoculation experiments have been made 



