GARPOPHTTA. 



197 



spore-bearing filaments, but here and there their resem- 

 blance to spore-sans is quite evident (Kg. 

 115"). When the spores are ripe, the ge- 

 latinous walls of the spore-sacs dissolve 

 and, the watery portions evaporating, 

 leave a dusty mass of black spores. The 

 spores germinate by sending out a short 

 fillament much as in the wheat-rust (Fig. 

 114, A and B), upon which minute 

 sporids are formed. It has been found 

 that when these sporids germinate upon 

 the epidermis of the very young corn- 

 plant they may penetrate it, and thus n(i_i? a 

 secure admission to the tissues of their t^^ee spore-bearing 



of Indian- 



host. 



filaments 



They cannot penetrate the epi- ^^^^ 



corn Smut, showing. 



dermis of older plants. S'sVrHlaSf 'rli^'. 



360. Other Smuts, as Wheat-smut or Magnified isoS times. 



Black Blast (Ustilago tritici) of wheat. Oat-smut (U. 

 avense), Barley-smut (U. hordei), and the Bunt or Stink- 

 ing-smuts (Tilletia tritici and T. foetens) of wheat, have a 

 structure and mode of development closely resembling the 

 foregoing. 



Comparing tlie spores of the Smuts witli those of the preceding 

 orders, we here consider them as sac-spores (ascospores), and the mass 

 of tissues in which they are produced, as a degraded spore-fruit. 

 The orderly arrangement of spore-sacs so evident in the Cup-fungi is 

 less marked in the more parasitic Black Fungi ; it is scarcely notice- 

 able in the Rusts, while in the Smuts it has entirely disappeared. 

 As the parasitism increases the structural degradation also increases. 



Practical Studies. — {a) Collect smutted ears of Indian corn. Mount 

 a little of the black internal mass in water and observe the spores. 



(6) Make very thin slices of young fresh specimens and examine 

 for parasitic and spore-bearing filaments. The outer tissues of the 

 distorted kernels are generally best. 



