1891.] PUBLIC DOCUMENT — No. 33. 209 



Farlow's pycnidia, above mentioned. They have oblong or 

 triangular cavities, lined with layers of small cells, from 

 which are produced large numbers of nearly colorless, 

 oval spores, about half as long as the pycnospores devel- 

 oped on gelatine. I have not been able to see that they 

 are developed on short threads, as is said by Dr. Farlow 

 to be the case with the spores in his pycnidia. Should 

 this form be proved to belong to the life cycle of the knot- 

 fungus, it will constitute its second pycnidial stage. 



The Hendcrsonida or stylosporic form described by Dr. 

 Farlow, which would constitute a pycnidial form, accord- 

 ing to present terminology, has also not been found even 

 to the extent of a single spore, though very careful and 

 thorough search has been made for it. It is also to be 

 expected that, if it were a genuine pycnidial stage of the 

 fungus, it might be produced on cultures, as the pycnidia 

 above described have been. This total failure to find the 

 form has led me to give it up as a feature in the develop- 

 mental histor}^ of Plowrightia morbosa. On consultation 

 with Dr. Farlow, he has kindly permitted me to say here 

 that he does not think there is sufficient evidence that this 

 form is really a stage of the knot-fungus, although it fre- 

 quently occurs with it. 



The summer spores, when sown on prune gelatine, swell 

 to an elliptical form, resembling that of the pycnospores, 

 and germinate by producing threads (Fig. 7). These also 

 form close, felted patches, and assume, after a time, the 

 characteristic dark color before mentioned ; and send up, 

 finally, erect threads, which bear conidial spores like those 

 from which they have grown (Fig. 8). No other form 

 was developed on these cultures, even after a long time. 



While considerable work remains to be done in deciding 

 the connection of doubtful spore forms, and in completing 

 the structural history of this pleomorphic fungus, the most 

 important work now remaining is the investigation of its 

 relations to its host plants. How it attacks them, how 

 the knots begin to develop, and the history of their devel- 

 opment, are the subjects which most need investigation 

 now. This Department has not heretofore been prepai^ed 

 for this stud}', but the necessary preparations have been 



