Apr. 29, igis Anthracnose of Lettuce 273 



much smaller than mature spores. No higher form of fructification is 

 known. 



PHYSIOLOGICAL RELATIONS OF THE CAUSAL ORGANISM 



GERMINATION PHENOMENA 



In order to study the germination phenomena, a suspension of spores in 

 very thin prune-juice agar was prepared, and a loopful of the preparation 

 conveyed to each of a number of cover glasses. These were inverted over 

 Van Tieghem rings and placed on the stage of a compound microscope. 

 After germination had started drawings were made every hour with the 

 aid of a camera lucida to show the progress of the development of indi- 

 vidual spores. The smear of agar on the cover glass was purposely made 

 thin enough to prevent the germ tube and later the mycelium from 

 growing out of focus. Complete drawings of the organism up to 40 hours 

 old were obtained in this way. The spores, when first produced, are 

 single-celled, hyalin, granular, with occasional oil drops, ovate or slightly 

 larger at one end, and measure, on the average, 7 to 8 by 2.5 to 3 /* (fig. 

 3, B). These small immature spores begin to swell up and a cross-wall 

 is formed, dividing the spore into two unequal cells, or less commonly 

 into two equal cells (fig. 3, A). The spore becomes constricted at the 

 septum, and may be slightly cur\^ed; but many of them remain straight 

 (fig. 3, C). When completely mature and ready to germinate, the spores 

 measure, on the average, 4 by 17 /x. Individual spores may exceed or 

 fall short of this size by a few microns, but they are fairly uniform in size. 

 When spores are placed in a favorable medium (prune-juice agar was used 

 with good results), development commences at once, the spores enlarge, 

 and in six to eight hours put forth a short, thick germ tube, which appar- 

 ently may originate at the sides or end of either ceil. This quickly en- 

 larges until it is the size of the cell producing it. When it is sufficiently 

 elongated, a cross-wall is formed, cutting off an additional end cell. This 

 in turn elongates, another cross-wall is formed, and thus cell by cell a long 

 strand of mycelium is formed. It may be four or five cells long two hours 

 after germination (fig. i, B). Sometimes an additional germ tube may 

 arise from the same cell (fig. i, B, c) or from the other cell of the original 

 2-celled spore (fig. i , B, f), which develops in the same manner as the first 

 one. Branches may spring from any of the newly developed middle cells 

 of the chain, and eight hours after germination a considerable ramifica- 

 tion is often observed (fig. i, E). In some cases chlamydospores are 

 formed (fig. i, B, d), but this phenomenon seems to depend upon the 

 nature of the medium. Thirty hours after germination a dense network 

 of mycelium has developed and numerous conidia are being formed. 

 These arise, one at a time, and separately — that is, not in chains — from 

 the apical end of short conidiophores (fig. 4). The conidiophores are 

 usually three or four cells long, and seem identical in the shape and size 

 of their cells vnth. ordinary vegetative mycelium. They were not ob- 



