INTERACTION'S OF PROTOPLASMIC MASSES. 12.} 



(g) One Line of a Clone Kept in Darkness, the Other Exposed 



to Light. 



Having funnel that related specimens could readily be made 

 negative to each other's protoplasmic fragments by adding 

 various substances to the culture medium in which one line was 

 grown, the following question arose: Are the changes thus brought 

 about due to the direct action of the added material, or to some other 

 causes? With this in mind, a series of experiments was begun 

 in which the same culture medium was used for both lines of a 

 clone, and in every other way they were treated alike, except one 

 line was placed in the dark while the other was kept before a 

 window. Thus, in one line the organisms were exposed to light 

 during the day, while light was entirely excluded from those 

 comprising the other, except for the short time required to trans- 

 fer them to new depression slides (a period of about two minutes 

 every other day). Four experiments of this type were conducted, 

 involving clones G, T, I , and V. In three out of the four cases, 

 the rate of reproduction was greater among the organisms kept 

 in daikness than among their relatives which were exposed to 

 light. However, it is possible that this was due to a greater 

 abundance of certain forms of bacteria upon which the Arccllce 

 fed; for it was observed that the bacterial growth was usually 

 very vigorous in the cultures which had been kept in the dark. 



The results obtained in these experiments may be briefly given 

 as follows: In clone G, line g and line g-d continued to inter-fuse 

 with each other's protoplasm until the I5th day (i6th genera- 

 tion); in clone T. the first negative reaction was observed on the 

 I2th day (12th generation); in clone U, shattering reactions 

 occurred between line u and line u-d on the i^th day (i5th gen- 

 eration); in clone V, cross-fusion between line v and line v-d 

 ceased on the I3th day (i5th generation). After two related 

 lines had once become negative, no further cross-fn-ion- occurred. 



In these experiments the average time required for two line- 

 of a clone to become so differentiated as to shatu -r each other'- 

 detached fragments of protoplasm was 13.25 day-, and 14.5 

 generations. While this is a longer period than was required 

 for the shattering reaction to be exhibited when sucrose, for 

 instance, was used as the differentiating factor, it i- s.; v ^ d.iy- 



