A'akr/I Stniii of Barley. lO? 



CHAPTEK XVI. 



Naked Smut of Barley. 

 {Ustilago nuda (Jens.) Kell. and Sw.) 

 It was first pointed out by Jensen ^ that there are two distinct kinds of 

 smut on barley. The one completely destroys the ear, being at first enclosed 

 in a thin silvery-looking membrane, which soon breaks, and the povrdery 

 spores are scattered by the wind as soon as mature. This is known as the 

 Naked smut (Plate X.) in contradistinction to the other, which is called 

 Co/ered smut, because the compact mass of spores is enclosed in the unbroken 

 walls of the ovary, and remains intact for some time, even after harvest. 

 Jhe heads of barley with Naked smut resemble those of the wheat when 

 affected with loose smut, and this resemblance extends even to the mode of 

 infection, which in both cases occurs in the flowering stage. 



Germination. 



The germination of the spores of U. nuda and U. tritici is quite different 

 from that of U. avenae and U. hordei. In the two latter, as has been shown, 

 a promycelium is formed, giving rise to conidia, while in the two former a 

 typical mycelium arises. The spore on germination produces a separate 

 germinal tube, which continues to grow at the apex and forms lateral branches 

 which in turn branch again, and so a spreading mycelium is developed without 

 the formation of conidia. This important difference in the mode of germina- 

 tion led Herzberg^ to propose a new genus — Ustilagidium — for the reception 

 of these two species. 



The germination of this species has been described by Kellerman and 

 Swingle,^ Brefeld,^ and Herzberg,^ among others. Spores obtained from 

 barley grown at Myrniong in 19()(i germinated freely in water and in a nutri- 

 tive solution in May, 1907. When grown in water a straight septate germ- 

 tube was first formed, the protoplasm of which was highly vacuolated, and 

 at first divided into four cells by transverse septa, then branches were spar- 

 ingly given off beneath the septa, sometimes at right angles, but generally at 

 an acute angle. The germ-tube sometimes became attenuated towards the 

 apex, and, although branches might be given off near the base, yet in no 

 instance was a spore met with producing two independent germinal tubes. 



In a nutritive solution the branching was much more copious. Brefeld^ 

 found that the filaments grew rapidly in various directions, and produced a 

 branching system like the mycelium of the higher fungi. The ends of the 

 filaments continued to grow in length, the contents passhig from behind 

 forward and formed very long tubes, which afterwards became septate. 

 Their branches were produced below the septa, and continued the process 

 until the central parts of the original mycelium were gradually drained of 

 their contents and carried to the circumference of the filaments. 



The spores do not long retain their germinating power, as it was found not 

 to have lasted for a year, and this, along with the absence of conidia, would 

 seem to indicate that the spore must germinate as quickly and directly as 

 possible in order to penetrate the stigmas of the flowers that are in bloom. 



Infection. 

 Brefeld' and Hecke^ have both recently shown that infection takes place 

 through the flower. It was found that when infection of seedlings was at- 

 tempted only negative results were obtained, and in every case sound healthy 



