George Raymond Gage 9 



such as is known in U. tritici, the embryo remaining free from invasion 

 and only the glumes being attacked. In fact, he says that the mycelium 

 does not penetrate the ovary and in no case can be found in, on, or under 

 the epidermis of it. He believes that the mycelium in the glumes is the 

 most important source of inoculum for seedling invasion, although over- 

 wintering spores, or perhaps sporidia, may play a small part. 



ARLAND'S STUDIES, 19 24 



The investigations of Zade were turned over to Arland (1924) for 

 further prosecution. In the main Arland 's results confirm those of 

 Zade. He also inoculated oat blossoms at pollination time and noted 

 that the spores germinated in the flower. This took place, however, in 

 four days instead of from fifteen to twenty hours as had been observed 

 by Zade. Moreover, the promycelia did not give rise to sporidia, the 

 temperature at the time being above 30° C. This is in keeping with the 

 recent observations of Bartholomew and Jones (1923:575) and of 

 Jones (1923: 590), who found 30° C. to be the maximum for sporidial 

 production. At lower temperatures Arland noticed sporidial produc- 

 tion in a few cases. Zade had suggested that resting sporidia might 

 play a role in seedling infection, but Arland refutes this possibility 

 since he was unable to keep dried cultures of sporidia viable for a 

 longer period than six weeks. The ungerminated spores, however, do 

 play an important role, in Arland 's opinion, since he was able to get 

 fairly high percentages of infection in certain variety tests when he in- 

 troduced spores between the glumes of mature oats prior to sowing. He 

 detected the development of mycelium not only in the glumes but also 

 in the remains of the stamens and the stigma. Incidentally he mentions 

 that he found it in a few cases in the epidermis of the ovary, By a more 

 extensive study of the mycelium he found that it often broke up into 

 biscuit- or dumbbell-shaped pieces which he called gemmae. He con- 

 cludes that the seat of overwintering mycelium is seldom the epidermis 

 of the pericarp, but is mostly the glume parenchyma and, without excep- 

 tion, the remains of the stamens and the stigma. 



With naked oats which he dusted with spores at blossom time, Arland 

 found that the mycelium which was produced wound itself among the 

 hairs of the earyopsis. // was seldom noticed in the epidermal cells. He 

 made variety tests with seed prepared in three ways: first, spores were 

 placed between the glume and the kernel prior to the sowing of the 

 oats ; secondly, deglumed kernels were dusted with spores ; and thirdly. 

 sporidia were introduced between the glume and the kernel. The av- 

 erage percentage of infection resulting in the first test was 29 per cent. 

 in the second 24.2 per cent, and in the third 5.1 per cent. Arena nuda, 

 var. chinensis, the glumcless oat used, proved to be much more suscepti- 

 ble than the glumecl varieties. A. strigosa and A. brevis were immune. 



