. The Biological bulletin. Biology; Zoology; Marine biology. CHEMOTAXIS IX SLIME MOLDS. II 301 The chemotactic response was \'irtually inclei)en(lent of the nuniher of ceHs in the attracting populations over the range of 400-5000 niyxamoehae. The cell suspensions from which these populations were derived contained X 10'' = 3 X 10' cells/nil. (Fig. 2). The responding drops came from a niyxamoehae sus- pension with 2 X 10' cells/ml. and contained 2000-4000 cells per population. All responding populations reacted positively at distances of mm. or less. The distance over which cells in 50%
. The Biological bulletin. Biology; Zoology; Marine biology. CHEMOTAXIS IX SLIME MOLDS. II 301 The chemotactic response was \'irtually inclei)en(lent of the nuniher of ceHs in the attracting populations over the range of 400-5000 niyxamoehae. The cell suspensions from which these populations were derived contained X 10'' = 3 X 10' cells/nil. (Fig. 2). The responding drops came from a niyxamoehae sus- pension with 2 X 10' cells/ml. and contained 2000-4000 cells per population. All responding populations reacted positively at distances of mm. or less. The distance over which cells in 50% of the responding populations were stimulated to move outside the droplet margins toward the attracting populations varied from mm. to mm. In a few cases sensitive niyxamoehae were attracted over distances as great as 4/ 5xl0/r ^00 600 800 1000 1200 MOO 1600 Distance of Attraction in N/licrons Figure 3. Four curves showing the percentage of responding populations that exhibit a response to developing aggregations in attracting poi)ulations of different densities, and the distances between these aggregations and the nearest margins of the responding popula- tions. The concentrations of the cell suspensions from which the attracting populations were derived are given. The diameter of the droplets containing the attracting populations was ca. mm. and that of the responding populations mm. The diameter of the control populations ( ) was mm. Results represent the average of three experiments. The delav hefore aggregation began varied with density. The onset of aggregation in populations with 5000 cells was ca. 5 hours after the deposition of the niyxamoehae. Populations with ca. 400 cells started to aggregate after 8-11 hours. With still fewer niyxamoehae the time of aggregation was consider- ably delayed. Like the chemotactic response, the duration of aggregation was also independent of the cell density. The number of populations that had star
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