134 BOARD OF AGRICULTURE. [Jan., 



prominence in the literature dealing with potato diseases in this 

 country, though it has been known and discussed for some time 

 in Europe. It is called the rosette disease because the green 

 vines often show the trouble by a rosette clustering of the 

 leaves. Finally some of the plants may turn a sickly yellowish 

 color and eventually die, but ordinarily the diseased condition 

 does not manifest itself above the ground. The trouble is 

 caused by a rhizoctonia, or sterile fungus that is carried on 

 the tubers. During the past two years this stage has been very 

 evident on the potatoes sold in this State. It shows as black- 

 ish growths of threads, usually compacted into sclerotia, or 

 superficial flattish masses, which are a quarter of an inch or 

 less in diameter and which occur more or less distinct or run 

 together over the tuber. Very often these escape notice or are 

 mistaken for dirt, but if the potato is washed and examined 

 while wet they become very evident. These compacted sterile 

 cells carry the fungus over the winter in a dormant condition, 

 but when the tubers are planted in the spring they develop a 

 mycelial growth that crawls up onto the young shoots. On 

 these, beneath the ground, the fungus often inflicts serious 

 injury by attacking the superficial tissues, sometimes com- 

 pletely girdling the stems with a dead area. This attack often 

 results in the death of the parts beneath, in which case new 

 tuberous shoots must be formed above the dead area. The 

 final result, then, is a crop of small potatoes or a greatly dimin- 

 ished yield. By the latter half of June and in July the fungus 

 appears just above the ground, surrounding the stems with a 

 grayish, mealy, rather inconspicuous growth for a distance of 

 an inch or two. This is the fruiting stage of the fungus, and 

 while not at all like the toadstools in appearance the manner of 

 its spore production places it with this group of fungi. Both 

 the fruiting stage on the stems and the rhizoctonia stage on the 

 tubers have been known in Europe, but their relationship was 

 not suspected. Only recently Mr. Rolfs of Colorado, while 

 studying the cause of the potato failure of that State, has 

 proved their connection. During the past season the writer 

 has observed the development of the fungus in this State and 

 has no doubt of the relationship of these forms. In some fields 

 from fifteen to twenty per cent, of the hills were observed with 

 the fruiting stage on the stalks. However, we were not able 

 to trace so serious injury to the infected plants as has been 

 reported in some other States. 



