I 88 MYCOLOGY 



American mycologists, pycnia (pyciiium), in which spermatia, or 

 pycniospores, are formed. Pycnia indicate the nature of the life cycle 

 and furnish positive characters for identification. Arthur has shown 

 that if pycnia and urediniospores are found arising from the same 

 mycelium, aecidia do not occur in the cycle; and if pycnia and telio- 

 spores are found there are neither uredinia nor secia in the life cycles. 

 These pycnospores are accompanied or succeeded by aeciospores 

 (aecidiospores), which appear in the cluster cups, or aecia in long chains. 

 The peridia of the different kinds of aecia are variable, and hence 



Fig. 64. — Spore forms of wheat rust, Pucainia graminis. A, Section through 

 barberry leaf showing pycnia on upper surface and secia on lower; B, two uredinio- 

 spores; C, germinating urediniospore ; D, teliosorus showing several teliospores; E, 

 single two-celledjteliospore ; F, germinating teliospore with four-celled basidium and 

 two basidiospores; G, basidiospore growing on barberry leaf. {Adapted from deBary.) 



mycologists have described four different kinds of form genera: Cceoma 

 = peridium absent; Mcidiiim = cup-shaped and peridium toothed; 

 Roestelia = peridium elongate and fimbriate; Peridermium = peri- 

 dium irregularly split and broken. Urediniospores (uredospores) 

 succeed the aeciospores and they appear in sori known as uredinia 

 Curedinium). Amphispores are special forms of urediniospores formed 

 in arid, or semi-arid climates and usually have a thick cell wall and a 

 persistent pedicel. They are in the nature of a resting spore. Meso- 

 spores are exactly of the same nature as the two-celled teliospores, but 

 they arise merely by the omission of the last nuclear division, and hence. 



