292 BULLETIN No. 189 [June. 



hypha. The partition walls are distant, often 120-200 //, apart. The walls now 

 possess the violet -brown pigment and in the lumen little or no protoplasm is ob- 

 servable. 



''The internal mycelium is likewise branched, septate, often associated into 

 loose strands, passing between the cells or traversing them. In the early stages 



of the disease, so far as reported, these internal hypha} are nearly colorless 



and are generally of less diameter than those constituting the external mat. 



" the hyphae constituting the external mantle may be uniformly dis- 

 tributed, as is the case usually when the fungus attacks fleshy roots or tubers, or 

 they may also form a number of aggregates having the appearance of loose or root- 

 like strands." 



The infection cushions are distributed^ over infected roots. ' ' The external 

 hyphae are for the most part similar to those of the general mycelium, but there 

 occur also branches in which the cells are short and swollen, sometimes resembling 



a short chain of spores The medullary portion of younger cushions is 



made up of finer, almost colorless hyphae, and it is this type which enters strand- 

 like the cortical tissues of the root, destroying particularly the cambium and 

 younger phloem regions. In the later stages of development it will be found that 

 the cushions seem to extend considerably into the cortex, and more of the hyphae 

 are colored." 



' ' The true sclerotia are flattened or rounded bodies varying in diameter from 

 a few millimeters to several centimeters. When mature they are of a deep violet- 

 brown and are thickly clothed with a persistent velvety felt, externally of the same 

 color as the root-investing hyphae, but darkening further in. Among the surface 

 hyphae of the sclerotia as well as of the 'infection cushions' are found chains 

 of enlarged cells quite distinct from the enlarged cells of R. Solani. The sclerotia, 

 as noted previously, are always connected with the root felt by large hyphal 

 strands. 



tf a sclerotium consists of fairly compact tissue made up of cells 



often considerably branched and sometimes curiously lobed. " 



DISTRIBUTION OF RHIZOCTONIA IN THE UNITED STATES 



In Table 1 is presented a list of those species and sub-species 

 which have been reported as being susceptible to R. Solani in the 

 United States. It is obvious that as long as investigations on this dis- 

 ease are continued, such a list cannot be regarded as complete or final. 

 It may be noted that plants belonging to the families Amaranfhacece, 

 Caryophyllacece, Cruciferce, Leguminosce, Solanacece, and Composite 

 are especially susceptible to this .fungus. Under favorable conditions 

 it can attack plants in these families at any stage, from seedlings or 

 cuttings to older plants, when grown either in the field or in the green- 

 house. About fifty important families of flowering plants are repre- 

 sented, several gymnosperms, and Equisetum, one of the Pterido- 

 phytes. The list includes a number of monocotyledons, which for- 

 merly were reported as being not susceptible to Rhizoctonia. Among 

 the dicotyledons are many annuals and perennials, including herbs 

 and woody plants, as well as most of the greenhouse and garden 

 plants, field crops, and weeds. 



R. Crocorum, as will be seen in Table la, has been reported so far 

 in this country from only a few scattered states. It is probable that 

 as investigations continue this fungus will be found in many other 

 localities. 



