May, 1909.] The Catalpa Leaf Spot. 511 



the spores were viable. The stress of other duties prevented a 

 repetition of the experiment and the negative results here secured, 

 throw but little light upon the source of infection. 



In addition to the fungi already mentioned as occurring upon 

 the leaf spots of the catalpa, the writer found a species of Epi- 

 coccum flourishing upon every spot in the leaves collected at 

 Columbus as well as upon every spot examined in the material 

 taken from the herbarium though it was not abundant upon that 

 labelled Phyllosticta catalpae. There is also present on the spots 

 in the leaves collected at Columbus and on those in herbarium 

 specimens labeled Macros porium catalpae a species of Cladospor- 

 ium, a fungus that, so far as the writer is aware, has not been 

 reported for the catalpa. These two fungi, however, are in all 

 probability soprophytes that have no part in producing the 

 spots upon the leaves. The results of this investigation tend to 

 show that the species of Alternaria ( = Macrosporium) occurring 

 on the catalpa is likewise a saprophytic form. Therefore, in 

 summing up the work so far as it has been carried the writer is 

 of the opinion that the disease-producing species is Didymos- 

 pheria catalpae, of which Phyllosticta catalpae is an imperfect form 

 and that the other species of fungi found upon the leaf spots are 

 saprophytic. Whether or not this is the true relationship exist- 

 ing among these different species of fungi remains still to be 

 proved — a task the writer hopes to find at some future time 

 opportunity to perform. 



EXPLANATION OF PLATE XXVI. 



The drawings were made with a Spencer microscope equipped 

 with a 3 mm. objective and an 8 x ocular (4 x ocular used with 

 No. 6). All are camera drawings made at table distance; 

 reduced one-half in reproductions. The magnification in the 

 microphotographs was not computed. 



Fig. 1. Conidial spores of Alternaria sp. on leaves collected at 

 Columbus. 



Fig. 2. Conidial spores from herbarium specimen labeled J^Iacro- 

 sporium catalpae. 



Fig. 3. Conidial spores from herbarium specimen labeled Phyllos- 

 ticta catalpae. 



Fig. 4. Conidiophores and conidia developed by placing in water 

 spots taken from leaves collected at Columbus. The number of spores in 

 the chains varied from 5 to 8. 



Fig. 5. Chain of spores found on herbaritim specimen labeled 

 Macros porium catalpae. 



Fig. 6. Ascus of Didymosphaeria catalpae drawn from a stained 

 section. 



Fig. 7. Ascospores of Didymosphaeria catalpae drawn from stained 

 material. 



Fig. 8. Microphotograph of a perithecium in a leaf spot. 



Fig. 9. Microphotograph of a section of a leaf spot showing a 

 perithecium of Didymosphaeritim catalpae at {a) and a pycnidium of Phyl- 

 losticta catalpae at (6). 



Fig. 10. Microphotograph of section of perithecium from which 

 Figvire 6 was drawn. 



