12 Journal of Agricultural Research vol. xx, No. i 



top of a hill. The field, which was only partly in rye, sloped at its west 

 end rather sharply to the south and at the east end sloped gently to the 

 south and east. The north side, the top of the hill, was fairly level and 

 protected by a wind-break of trees. To the east and west also there were 

 trees. The top or level part of the hill was sown with winter rye and the 

 sloping parts with second-year alfalfa in which barley had been the nurse 

 crop the preceding year. On the old barley stems left in the alfalfa 

 field were a considerable number of G. saubinetii perithecia with viable 

 spores. The only wind that could reach this field was from the south. 

 The rye field was as uniform as could be expected in all respects except 

 slope. The degree of head blight infection, however, was very different 

 in the different parts of the field, although it was only a small and narrow 

 strip of land. Blight was practically absent in the west part, which was 

 surrounded on the north and west sides by wind-breaks. However, on 

 the southwest edge there was considerable blight infection among the 

 plants that were immediately next to the alfalfa field in which, as stated 

 above, G. saubinetii was present and the slope was very steep. The 

 east part of the field, which was protected on the north and east sides 

 by wind-breaks, had, on the other hand, up to 5 per cent of blight, not 

 only among the plants next to the alfalfa field but also throughout its 

 south half, while its north half was free from blight. Knowing of no 

 other factors that could account for this difference, the writer is inclined 

 to think that the following is the possible explanation of the distribution 

 of the disease. The west end of the field bordering on the alfalfa field 

 where the slope was steep was infected only through the area next to 

 this field, because the wind, lifting the spores from the alfalfa field, could 

 not raise them into the upper air currents and so over the hill but deposited 

 them against the slope before they could reach the rye plants on the level 

 ground. Thus, only those rye plants were infected that were next to 

 the alfalfa field. In the east part of the field the situation was different. 

 The slope there was gradual and the spores needed to be lifted only 

 several feet in order to be on a level with the rye field. Thus they could 

 be easily carried to the rye plants even by the slightest air currents; 

 and for this reason, perhaps, the infection in this part of the field was 

 greater, although even here it was restricted to that half of the field 

 which bordered on the alfalfa field. This indicated that the source of 

 infectious material was the alfalfa field and that the infection extended 

 onlv as far as the topographical conditions permitted the wind to carry 

 the spores. 



BY RAIN 



The conidia produced at first are usually very loosely attached to the 

 mycelial growth and are easily detached from it by wind, insects, and 

 other agencies, while the conidia formed later and in pionnotes, as is 

 commonly the case, stick together. However, if a drop of water is 

 placed on the pionnotes the spores are set free with great rapidity and 



