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A TEXTBOOK OF BOTANY 



[Ch . X 



produce a mycelium which develops uredospores and teleuto- 

 spores, as already described. Thus this plant includes in 

 its life history three stages, two hosts, and four kinds of 

 spores aside from the spermatia (or pycnospores) . 



While such is the life cycle of the Wheat Rust in localities 

 where the Barberry occurs, that host may be omitted in 

 case Winter Wheat is grown, for uredospores can hibernate 

 in the young plants over winter, and re-infect the fields in 

 the spring. Furthermore, varieties of this Puccinia appear 

 to have been evolved with an aecidial host other than Bar- 

 berry. The parasite is a particularly difficult one to combat, 

 and cannot be destroyed by any known method which will 

 not ruin the host plants. The greatest hope for its sup- 

 pression lies through the breeding of immune varieties. 



To this order belongs also the White Pine Blister Rust 

 (Cronartium ribicola), recently introduced from Europe, and 

 now threatening to rival the Chestnut disease in destruc- 

 tiveness. The two hosts are the Currant or Gooseberry and 



the White Pine, and, 

 contrary to the case 

 with Puccinia, the aeci- 

 dial stage, on the Pine, 

 is much the more de- 

 structive. For a year 

 or more after infection 

 the Pine shows no ex- 

 ternal sign, but then 

 the mycelium destroys 

 the cambium and inner 

 bark, and therefore 

 kills the branch. On the bark now appear white blisters 

 which break open and expose the yellowish aecidial spore 

 masses. These secidiospores do not infect Pines, but only 

 Currant or Gooseberry leaves, in which the mycelium de- 

 velops, and produces, on the under side, powdery yellowish 

 clusters of uredospores. These are disseminated by the wind, 



Fig. 326. — Tremella mesenterica; X f. 



The body is gelatinous, and the basidia 

 form on the surface. (After Tulasne, from 

 Bennett and Murray, Cryptogamic Botany.) 





