128 Mortier F. Barrus 



weather and on temperature conditions. The writer's numerous obser- 

 vations are in accord with this as regards the production of typical 

 anthracnose lesions. Temperature appears to have some influence on 

 the length of the incubation period; also, the period varies considerably 

 with the different varieties of beans under the same conditions. Schaffnit 

 (1920) finds that the incubation period, and also the period between 

 infection and spore formation, differ with different varieties. 



Reproduction of the fungus within the host 



At about the time when the cell walls collapse to form a canker, or 

 even earlier in many cases, the mycelium at certain points develops 

 abundantly in the epidermal cells and in those just beneath, forming a 

 stroma of closely crowded, many-septate hyphae. The host cells at these 

 places are so flattened that it is difficult to observe them (Plate II, 2), 

 From this pseudoparenchymatous tissue arise short, more or less erect, 

 conidiophores, from 15 to 20 ix long and from 4 to 5 /x broad, at the apex 

 of each of which is borne a small conidium rounded at the top and drawn 

 out to a point at its attached end. This conidium enlarges somewhat 

 before becoming detached. The conidia are formed by the constriction of 

 the upper end of the conidiophores, as described in connection with ger- 

 mination in culture media. Spore after spore is produced by the conidio- 

 phore; the cuticle, which has been pushed up to form black pimples in 

 the canker as the conidiophores elongate, is soon ruptured, and the spores 

 emerge in a gelatinous pink mass (Plate I, 1) Frank (1883 b: 513) de- 

 scribes the formation of the stroma and the production of spores enveloped 

 in slime, the rupture of the cuticle, and the behavior of the spores thereafter. 



These first acervuli formed at the center are followed by the production 

 of others as the lesion enlarges. In a single lesion there may be fifty 

 or more acervuli, in which thousands of spores are produced. Edgerton 

 (1910:12) estimated that on a badly spotted pod, from 110,000,000 to 

 115,000,000 spores had been produced. After washing these off and 

 placing the pods in a moist chamber for twenty-four hours, he found that 

 about 50,000,000 more spores were produced, and he concluded that a total 

 of from 500,000,000 to 1,000,000,000 spores may develop on some pods. 

 If the weather remains moist and cool, the conidiophores will continue 

 to produce conidia; but during dry weather the spore masses harden 

 down over the acervulus and spore formation ceases.' 



