Bean Anthracnose 127 



penetration. It seems that this is the really critical time in the develop- 

 ment of the fungus, for it must overcome the protoplasm of the host 

 cell before it can continue its development. Varieties of beans immune 

 to certain strains of Colletotrichum lindemuthianum probably owe this 

 immunity to the inability of the infection hypha of the fungus to overcome 

 the resistance offered it by the protoplasm of the host cell. The writer 

 (Barrus, 1918:594) has shown that some such varieties, on inoculation 

 with such a strain, have shown on their pods and stems a slight but dis- 

 tinct specking, as though the fungus had entered the tissue and killed 

 a few cells but was unable to proceed farther. This specking did not 

 appear on the pods of plants not inoculated. 



Once the fungus has established itself within the host cell, the hyphae 

 extend horizontally and diagonally into other cells, penetrating the cell 

 walls of the host as they come into contact with them (Plate II). 

 In some cases the hyphae enlarge when in contact with the cell wall, and 

 a small hole is formed through which projects a slender tube that at 

 once enlarges after passing through. As many as twelve hyphae have 

 been observed penetrating a single cell (Plate II, 4). Growth within 

 the host is rapid, particularly if the tissue is young and tender. The 

 protoplasm of the host cell is killed and turns brown soon after being 

 attacked. The walls collapse, and after from four and one-half to seven 

 days a lesion may be observed on the surface. 



There seems to be a great difference of opinion as to the length of the 

 period of incubation. Frank (1883 a: 33) noticed the beginning of a 

 browning of the epidermis at separate points on the pods twenty-four 

 hours after inoculation was made. This browning had extended by 

 the following day, and five days after inoculation Frank obtained the 

 first spores in the new lesion. Scribner (1888) states that the cells become 

 discolored almost at once after the hyphae enter. Halsted (1892:284) 

 found a spot on an otherwise healthy pod thirty-six hours after inoculating 

 it in the laboratory under the most favorable conditions. Pammel and 

 King (1909) report having obtained an anthracnose spot thirty-six hours 

 after inoculation. Dey (1919) claims that early specking appears on 

 a pod when tap water is substituted for infection drops, and thinks it 

 due to osmotic disturbances. Edgerton (1910: 14) finds from inoculations 

 made on plants in the greenhouse and in the field that the period of 

 incubation ranges from four and one-half to nine days, depending on the 



