OLIVE : MONOGRAPH OE THE ACRASIEAE. 
487 
stalk shows the torsion induced by the spiral ascent. In order to 
determine whether the force of gravity may have caused the coil in 
the case of Dictyosteliiim purpiireum^ cultures were rotated in a 
horizontal plane, so that the nutrient agar surface was placed verti- 
call}’’, and both gravity and light forces were thus overcome. Con¬ 
stant rotation for weeks produced no perceptible effect on the 
spirally moving pseudoplasmodia, for the phenomenon was as pro¬ 
nounced as ever and occasionally the colonies even reversed the 
usual right to left direction and twisted from left to right. The 
stalks usually straighten out on maturing and lose the spiral appear¬ 
ance, thus simulating again the phenomena observed in twiners 
among higher plants. 
General Methods. 
Pure cultures have been utilized as far as possible in making 
this study of the life history of these organisms. Cultures of dung 
and of decaying substances in general have been kept in covered 
crystallizing dishes or in tin boxes, and as forms of the Acrasieae 
appeared they were transferred by means of a platinum needle to a 
slant culture tube. The media used for culture tubes included an 
attenuated dung decoction, horse dung being usually employed, a 
potato decoction and a pejjtone nutrient medium, besides several 
standard culture solutions, such as Pfeffer’s solution for cultivating 
fungi. These were stiffened with from about 1% to ^.5% of agar- 
agar, and sterilized. The best results were obtained with the horse 
dung decoction tubes and with the peptone nutrient medium. 
While all of the Dictyosteliaceae usually grow luxuriantly upon 
either of these substrata, certain sj^ecies seem to prefer the peptone 
medium, Dictyosteliiim, piirpureum, for example, growing with 
astonishing vigor on the latter medium. In a strong dung decoc¬ 
tion, or in one that is too weak, the fruit bodies do not develop 
well, if at all. Even in tubes made with nothing but distilled water 
and agar, however, fructifications appear in small numbers, some 
nourishment being doubtless obtained from the gelatinous substance 
of the alga. 
Sappinia, as mentioned above, failed to form aggregations on cul¬ 
ture tubes, while Guttulinopsis produced fructifications in abundance. 
