THE RUSTS OF NOVA SCOTIA. ERASER, 325 



(1880-1891) studied the genus Gymnosporangium in this way, 

 and Arthur began culture work in 1899 and has carried it on 

 to the present time. 



The method used in culture experiments is usually as fol- 

 lows. Hosts or suspected hosts are grown from seed or trans- 

 planted into pots and kept in some suitable place. Teliospores 

 that have been wintered are germinated in a moist chamber, 

 and the basidiospores are then applied to the leaves of the 

 plants, which are then kept under a bell jar for a few days. 

 If successful the pycnia usually appear in 8 to 12 days. Infec- 

 tion by basidiospores is usually more marked than by aecio- 

 spores or urediniospores ; a rich infection usually follows and 

 is not likely to be confused with accidental infection. The 

 writer has obtained the best results from first placing the leaves 

 or parts bearing telia in a moist chamber till the teliospores 

 had germinated, usually twelve or fifteen hours. These were 

 then suspended above the suspected aecial hosts so that the 

 basidiospores would fall on the leaves, the whole was then 

 covered with a bell jar for a day or two. 



The easiest and most successful way to obtain clues to the 

 alternate hosts is to watch for the appearance of aecia in the 

 spring and early summer. If they are found thickly covering 

 the leaves or parts of a plant, usually search in the immediate 

 vicinity will reveal plants bearing telia, and if the teliospores 

 are or have germinated, it will be evidence that the aecia 

 and telia are probably connected, especially if no other rust 

 can be found near. These clues can be tested at once by 

 cultures if viable material can be found ; if not, the test can 

 be made in the following season, when it may be easier to 

 collect viable teliospores. 



Association of Spore Forms. 



As has alreadv been stated, the spore forms appear in a 

 definite order. Thus, when the cycle of development is com- 

 plete, the germinating teliospores give rise to the basidiospores, 



