CRYPTOGAMS 



321 



364. Connection between barberry and wheat rust. — 

 With the discharge of the aecidium spores, the part of the 

 Hfe cycle of the fungus spent on the barberry conies to an 

 end, and it is ready to begin the uredo-teleuto stage over 

 again as soon as it finds a suitable host. Where there are no 

 barberries, it is capable of propagating without them, either 

 by adapting itself to some other host plant, or by omitting 

 the 2ecidium stage al- 

 together. The para- 

 sitic habit being an 

 acquired one, the 

 fungus, like some ani- 

 mal organisms that 

 we know of, can often 

 be "educated " by 

 force of circum- 

 stances into tolerat- 

 ing, and even thriv- 

 ing upon, foods which 

 under other circum- 

 stances it would re- 

 ject. The wheat rust 

 is known to be ca- 

 pable of propagating 

 year after year in the F'«- ^^g- - a spedes of " cedar apple '• {a,m- 



•^ '' nosporangiim) , showing the uredo-teleuto stage of 



Uredo stage, the the apple rust fungus. (From a photograph by 



spores surviving I'-f- 1"^ J^- Lioyd.) 



through the winter on volunteer grains and grasses ; and in 

 no other country in the world does rust do greater damage 

 to the wheat crop than in Australia, where the barberry 

 is practically unknown. This power of accommodation 

 possessed by many parasites is one of the difficulties the 

 agriculturist has to contend with in the development of rust- 

 proof varieties. 



365. Pol3miorphism. ^ Plants that pass through different 

 stages in their life history are said to be pulyniorphic, that 



