202 



Bulletin 132. 



aflfected were in an advanced state of growth. Many of the lower 

 leaves were brown and wilted, while the disease seemed to spread 

 rapidly to the younger leaves as they unfolded in freshness and 

 vigor. The spots on the vigorous blades were characteristic of 

 the disease popularly known as "celery blight," and a micro- 

 scopic examination confirmed this, show- 

 ing the causal fungus to be Cercos- 

 pora Apii. This is one of the first 

 celery diseases to make its appearance 

 either in the seed-bed or in the field. It is a 

 well known pest in Europe, and in this 

 country it seems to have received spasmodic 

 attention for nearly fifteen years. Begin- 

 ning on the outermost green leaves, it 

 appears in spots more or less circular, gray- 

 ish-green at first, and becoming brown and 

 ashen. In the early stages of the disease 

 there is a well defined spot with slightly 

 raised border ; but when the spots become 

 numerous on a leaf, the latter begins to turn 

 yellow, and subsequently the fungus devel- 

 ops abundantly its fruiting growth in indefi- 

 nite areas, thus giving the characteristic 

 ashen spots of indiscriminate form. The 

 filamentous vegetative organs of this fungus, 

 like most parasitic fungi, grow within the 

 tissues of the leaf, and soon minute fertile 

 filaments, or hyphae, are protruded in slight 

 fascicles through the pores, or stomates, of 

 the leaf. These fertile hyphae (or fruiting 

 filaments) as seen under the microscope are 

 illustrated in Figure 48, a, b, and^*; and 

 here it is also seen that these hyphae bear hyaline reproductive 

 bodies, the spores, or conidia, e and d. Falling upon other leaves 

 with suitable moisture, these conidia germinate by the protrusion 

 of delicate thread-like tubes, and these tubes efiect an entrance 



48. — Microscopic charac- 

 ters of the early blight. 



*This figure was drawn by Professor Geo. F. Atkinson, and used by hijD 

 in Bulletin 49 of this Station. 



