14 BULLETIN 1417, U. S. DEPARTMENT OF AGBICTJLTTJBE 



All attempts to germinate the spores of the conidial stage failed, 

 in spite of the fact that spores of all ages were used under many 

 varied conditions, with a large number of soil and plant decoctions, 

 stimuli, and other methods used in spore germination. In a few in- 

 stances the spores obtained from newly formed spore mats placed 

 in distilled water and held in an ice box became slightly swollen, 

 and some semblance of a germ tube was produced; but otherwise 

 no reaction of any sort occurred. 



The conidial stage of Ozonium seems to be very similar to the 

 Corticium stage of Rhizoctonia solani Kuhn. In both instances 

 the spore stage does not appear to be necessary in the life cycle of 

 the fungus, as both organisms can maintain themselves from year 

 to year by means of the sterile mycelium. The Corticium spores are 

 very difficult to germinate ; in fact, the only successful method devel- 

 oped has been the placing of spore-bearing material over an agar 

 plate, and only a few of the mature spores which fall on the agar 

 germinate. Although the germinating Corticium spores develop on 

 agar to produce the sterile mycelium of Khizoctonia, which in turn 

 can cause infection, no one has yet succeeded in infecting susceptible 

 plants with the spores. As in the case of Corticium vagum B. and C.,. 

 it is doubtful whether the conidia of P hy mat o trie hum omnivorum 

 will be found of any importance in the propagation, development, 

 and spread of Ozonium. 



PERFECT STAGE 



Shear (7) has recently described a perfect stage of this fungus 

 which he has named Hydnum omnivorum, based on the connection 

 between typical Ozonium hyphse and the formation of a hymenium 

 of the above-described Hydnum. 



In this connection it might be stated that during the summer, and 

 especially after every irrigation at Sacaton, Ariz., a number of small 

 (2 centimeters) fan-shaped mats were found growing on the soil 

 in well-shaded spots under cotton plants. Most of these mats were 

 of an orange-yellow color. A number of these were dug out and 

 found to arise from a rhizomorphic mycelium very similar to 

 Ozonium strands on the old cotton roots invariably found under 

 these mats. Specimens were sent to E. A. Burt, of the Missouri 

 Botanical Gardens, who identified them as resupinate Hydnums. 



Perhaps these specimens found so abundantly at Sacaton are the 

 same as those described by Shear. Of course, final proof of this 

 connection, as Shear states, must be obtained by germinating the 

 spores of the Hydnum to produce the typical mycelium of Ozonium. 

 It is interesting to note in this connection that the soils of the South- 

 west seem to be particularly adapted to the growth of many rhizo- 

 morphic fungi. 



INOCULATION EXPERIMENTS 



Of the many attempts to produce infection with Ozonium by those 

 who have studied this disease, very few have been successful. Tau- 

 benhaus and Killough (8) reported the results of successful inocu- 

 lations on 10 young plants of cotton. While no doubt the organism 

 caused a wilting of the plants and could be recovered in culture, the 

 plants were grown under very abnormal conditions. So far no one 



