THE FUNGI WHICH CAUSE PLANT DISEASE 477 



It consists of a close bed of short conidiophores. Figs. 371, 379. 

 Acervuli may be small or large, subepidermal, subcortical or super- 

 ficial and may or may not be provided with hairs (setae) Fig. 370, 

 of various kinds. An acervulus with a well marked basal stroma 

 is known as a sporodochium. Fig. 435. If the sporodochium stalk 

 is markedly developed the structure becomes a coremium. It is 

 sometimes quite difficult to distinguish between a pycnidium 

 with an extremely large ostiole, or one with a very thin wall, and 

 the acervulus. For such purposes thin longitudinal sections are 

 toost useful. 



Hyphse are conidiophores which grow free for some distance 

 above their supporting substratum and in more loose form than in 

 the acervuli, so that the terminal parts at least stand out as sep- 

 arate threads. Figs. 383, 384, 396, 410. 



The hyphse maybe simple and short, or long and much branched. 

 When the hyphse are very short and closely crowded to form a 

 sporogenous cushion the condition of an acerviilus is approached 

 and confusion arises. 



The conidia borne in the pycnidia, acervuli or on the hyphse are 

 of as various forms and types as is well conceivable and are made 

 the chief basis for subdivision of orders into form-genera. They 

 may be simple or compound, of almost any color, and may be borne 

 in bisipetal succession in chains, or solitary, or in groups at the 

 apices of the conidiophores. 



The following scheme of Saccardo presents the confessedly 

 artificial groups into which conidia may for convenience be divided. 



Scheme of Spoke Sections. 



Amerosporse: spores 1-celled, not stellate, spiral or filiform. 



Hyalosporae: spores hyaline or clear, globose to oblong, contmuous. 



Phaeosporae: spores dark, yellow to black, globose to oblong, con- 

 tinuous. 

 Didymosporse: spores, 2-celled. 



Hyalodidymae: spores hyaline, 3-celled. 



PhaeodidymsB: spores dark, 2-celled. 

 Phragmosporae: spores 3 to many-celled by cross septa. 



Hyalophragmise: spores hyaline, 3 t6 Jnaiiy-celled. 



Phseophragmia: spores dark, 3 to many-celled. 



