258 Diseases of Greenhouse Crops 



up of compact clusters of oval or curved branches 

 originating from a common center. This vegetative 

 body occupies a single cell of the affected prothallium, 

 later putting out a slender germ tube which pierces 

 the adjoining intervening wall, forming clusters of 

 oval mycelial branches which become rounded and 

 play the part of resting spores. Each of them may 

 germinate by sending out a short germ tube at the 

 tip of which a conidium is formed. When mature, 

 the latter breaks off and is capable of germinating. 

 Upon coming in contact with the host the conidia 

 germinate by sending out a flask-shaped tube which 

 comes close to the wall of a cell. The protoplasm 

 of the conidium now migrates into the inflated germ 

 tube. The latter produces a slender tube which 

 bores its way into the cell of the prothallium, where 

 it swells and grows in a fashion previously described 

 (fig. 55, a to d.). Completoria complens attacks 

 prothallia of the following ferns: Aspidium (Cyro- 

 tominum) falcatum, Pterisargyria, and Pt. cretica. 

 Very little is as yet known of its method of control. 



Phyllosticta Leaf Spot 



Caused by Phyllosticta pteridis Hals. 



Symptoms. Ornamental ferns, such as Pteris 

 cretica var. Magnifica are especially susceptible. The 

 first symptoms of the spot disease is loss of the nor- 

 mal green in the frond. This is soon followed by the 

 appearance of the ashy-gray spots surrounded by a 

 border that is either purple or brown. Within the 



