1893.] MICRUSCoriCAL JUUllNAL. 197 



bor the spores germinate (Plate III, fig. 5b), each cellbeiuf? ca- 

 pable of producing a germ tube. According to Von Thuemen 

 this cnter.s; the beet leaf by way of the stomata. Once in the 

 interior of the leaf a vigorous mycelium is produced, which in 

 a short time gives rise to the brownish several-celled, fascicled 

 and occasionally branched thread.s (conidiophore.s,) which bear 

 the long needle-shaped many-celled nearly colorless spores. 



These spores which pass into the soil with decayed leaves, are 

 capable of infecting young beet leaves the following spring. 



V. — The Violet Root Fungus. 



In 1855, Kuehn called attention to a serious root-rot of alfalfa, 

 carrots and mangolds, in which a violet mould closely invested 

 the roots. The disease caused dead patches to form in the 

 field. The fungus causing the disease is known as Rhizoctonia 

 medicagims. It is the sterile mycelium of the perfect fungus 

 Leptosphcerta circinans. This fungus has been found on alfalfa 

 in Nebraska. 



Kuehn has described a second root-rot disease of the beet, 

 Rhizoctonia betse. Our fungus appears to belong to this species. 

 This fungus is very destructive in Germany, where it not only 

 affects large beets, but young seedlings as well. This disease is 

 said to produce on the surface of the beet brown spots which 

 speedily enlarge. The diseased tissue is marked by producing 

 a pale brown zone. The mycelium of the fungus advances in 

 the tissue of the plant, causing a disorganization of the cells of 

 the beets, the fungus apparently throwing oft" a ferment which 

 prepares the way for the fungus. Sclerotia were also observed. 



The Iowa disease manifests itself by a gradual dying of the 

 plant. In plants where the root is not fleshy, death is sudden. 

 This is also true of other root-rot diseases, especially root-rot of 

 cotton caused l)y Ozonium auricomum and ihe violet root fungus 

 {Rhizoctonia medicaginis,) when it affects alfalfa. The leaves of 

 diseased beets are of pale color and more lax than in adjoining 

 plants. However, these are not always the external manifesta- 

 tions, since diseased beets occur where there are no external 

 symptoms. Like other root-rot diseases it occurs in patches 

 spreading mostly in rows, though in some cases there is a ten- 

 dency to spread radially. It may afiect a single beet in a place, 

 or a dozen or more are diseased. Early in September some of 



