PRINCIPAL GROUPS OF PLAXTS. 



67 



tinues for some time. On germination they bud like yeast, form- 

 ing new conidia, or when nutrition is not abundant they may 

 form a mycelium, which is usually the case when they germinate 

 on a host plant. 



Corn Smut. — One of the Smut Fungi, namely, Ustilago 

 Maydis, which develops on Indian corn (Fig. 39), is used in medi- 



00% 



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Fig. 40. Spores of various Smuts. I, Ustilago loyigissima growing on the reed meadow- 

 grass {Panicularia americana); 2, Ustilago Maydis from Indian corn {Zea Mays)\ 3, Ustilago 

 Oxalidis on the yellow wood-sorrel {Oxalis stricta) ; 4, Ustilago utriculosa on the Pennsyl- 

 vania persicaria {Polygonum pennsylvanicum). 



Fig.- 40a. Germination of spores. 5, Ustilago utriculosa, in water, showing promy- 

 celium and sporidia; 6, Doassansia opaca from the broad-leaved arrow-head {Sagittaria 

 latifolia) in water, showing promycelium, sporidia, and secondary sporidia which are falling 

 off; 7, Ustilago Avenos from oat {Avena sativa) in horse dung, showing promycelium, and 

 lateral "infection threads" or hyphae; 8, germination of a sporidium of Ustilago Sorghi into 

 an infection thread; 9, small portion of a group of sporidia developed from promycelium 

 of Tolyposporium Eriocauli on potato agar; 10, cross-section of epicotyl of broom-corn 

 infected by Ustilago Sorghi showing mycelium ramifying through parenchyma cells 

 of the cortex. — After Clinton. 



cine. It forms rather large gall-like masses on all parts of the 

 plant, including the root, stem and leaves, and both staminate and 

 pistillate flowers. The spores (Fig. 40) are at first a dark olive- 

 green, but on maturity are dark brown. They are sub-spherical, 

 have prominent spines, and vary from 8 to 15 microns in diameter. 

 They do not germinate at once, but on keeping them for six 



