ORDER MONILIALES (hYPHOMYCETEAE) 589 



cases well-developed phialides are present but in other cases the conidia 

 appear to be more properly "radulaspores." They may be single or in 

 chains, one-celled or septate, hyaline, or brown. Probably the fungi with 

 this type of conidiophore are not closely related. Among such fungi are 

 Gonatorrhodiella, Arikrobotrys, Gonatobotryum, Gonatorrhoduni, Gony- 

 trichum. (Fig. 196B.) 



The genus Verticillium is named because of the whorled arrangement 

 of the branches of the conidiophore. The conidia arise singly at the tips of 

 phialide-like branchlets. V. alboatrum Reinke & Berth, is the cause of a 

 disease called "hadromycosis," producing death in very many plants, 

 woody and herbaceous, e.g., species of Acer, Solanum tuberosum L., 

 Dahlia, etc. No perfect stage is known. (Fig. 196A.) Botrytis has branched 

 conidiophores, but these are not verticillate, nor swollen at the ends. 

 Various serious diseases of plants are caused by species of this genus. 

 Some species form sclerotia in the host tissues. Some of the Sclerotiniaceae 

 (Ascomyceteae) have a Botrytis stage, but for the majority of the species 

 of Botrytis no perfect stage is known. The genus Phymatotrichum differs 

 from the foregoing in that the terminal spore-bearing portions of the 

 branches of the conidiophore are somewhat swollen. P. oinnivorum (Shear) 

 Duggar is the conidial stage of the fungus causing the root rot of cotton 

 and many other plants in Texas and some adjacent states. Closely related 

 is the genus Oidium, more often known as Rhinotrichum. (Fig. 197A.) All 

 of the foregoing genera are hyalosporous, i.e., have one-celled conidia 

 which are colorless or light-colored (except as noted for Aspergillus). 

 Among the Hyalodidymae, Trichothecium, and Cephalothecium both pro- 

 duce somewhat pear-shaped hyaline or pale pink spores that are two- 

 celled, the basal cell being smaller than the terminal one. They are mostly 

 saprophytic although C. roseum Corda enters the fruit of the apple 

 through the lesions caused by the scab organism {Venturia inaequalis 

 (Cke.) Winter) and causes rot. In Cephalothecium the conidia are produced 

 in heads while in Trichothecium they are single at the tip of the conidio- 

 phore. Arthrobotrys bears similar conidia but they are clustered at various 

 swollen intercalary cells of the unbranched conidiophore. Some species 

 are saprophytic, but Drechsler (1937) described six species parasitic upon 

 terricolous nematodes which are caught in net-like structures of the 

 mycelium. Mycogone perniciosa Magn. is a dangerous pest in the com- 

 mercial culture of the common mushroom {Agaricus campestris L. ex Fr.). 

 Its short conidiophores, lateral to the hyphae of the mycelium, bear 

 terminally single conidia, two-celled and constricted between the upper 

 (larger) and lower cells. These conidia may be slightly roughened. They 

 are sometimes considered to be a form of chlamydospore since on slender 

 upright hyphae there sometimes occur verticillate branches bearing small 

 one-celled spores. Other Hyalodidymae growing upon fungi are Diplo- 



