322 THK Itl'SI'S OF \ti\A SCOI'IA. Fl! ASF.K. 



germinate unless ex^wsed to the weather for some time. If 

 kept inside dnring the winter germination does not follow even 

 if placed nnder favourable conditions. 



After c'X[)o.sure to the weather for some time, they usually 

 germinate under favourable conditions, though germination is 

 somewhat uncertain. A tube emerg-es from the germ pore and 

 soon divides into four, each segment is called a basidium and 

 produces on a sterigina a small, usually hyaline spore. These 

 spores, called basidiospores (sporidia), when they reach a suit- 

 able host germinate, the germ tubes make their way through 

 the epidermis and infection results. 



When the teliospores germinate at once usually the other 

 spore forms are suppressed. They arc not lost, however, as 

 they occasionally make their appearance. When the telio- 

 spores germinate at once the germ-tnbe of the br'^idiosporc is 

 said to enter at the breathing pore. 



Mesospores. 



In many rusts of the genus Puccinia, beside the usual two- 

 cteflleck spores large numbers of the single-celled ?vporos are 

 formed. These resemble the teliospores and funetion like 

 them, the only difference being in form and the nuuiber of 

 cells. They are called mesospores. They are common, espec- 

 ially in some species of the grass and sedge rusts. The presence 

 of these one-celled spores seems to indicate a close relationship 

 to the genus Uromycea. It is jiossible lliaf the genus Piieclnia 

 clevelojied from Uromyces. 



JT cteroecism . 



Many rusts pass part of their lif(>. cycle on one |)lant ami 

 part on another, while in some species the whole life eycle is 

 confined to one host plant. Those l)elonging to the fonner are 

 called heteroecious species and the latter autoecious species. 

 In heteroecious species one host plant bears the pycnia and 

 aeeia. the other the uredinin anrl telia. TTsunllv the lio^t i)lants 



