m he only apparent explanation of the group orientation is '.hat 

 of a diffusion gradiant of some substance emanati^ng from a growing 

 spore, or of some substance being used up by it. A continuation 

 of the inve/stigati ^n of this problem will b3 an attempt to dis- 

 cover a substance or substances which can so effect the dividing 

 nucleus of the egg cell that its unequal distribution on *M sides 

 of the cell will orient the qxis of the spindle, The effect of bub- 

 bling carbon dioxide or_ oxygen through one end of a culture will 

 be tried as being the most probable factor^ involved. 



A striking phenomenon which seems to be further evidence of 

 the power of a chemical stimulus to orient the spores was found in 

 three different cultures. ?.mall pieces of a foreign substance, 

 apparently sand, caused the orientation of the spores adjacent to 

 astey'ith the result that the rhizoids all extended inward towards 

 t: e substance. This material was present in too small amounts for 

 chemical analysis. A search for some difficultly soluble substance, 

 or an insoluble substance which might be sligBiJfly soluble in the 

 weak carbonic acid produced by the growing spores, which, when added 

 to the cultures , might orient the eggs adjacent to it, has failed 

 to brin* any positive results. They do show ^however, that the phenom- 

 enon is not due to a contact stimulus. "Ehe^//^ substances tried 

 W3repcheelite/ Ca^o^Oj; 'Magnetite/ F Qj J, Ba ite/Ba^So), Casser-ite 



n oAnornblend, tfubellite, beach sand, granite, and silve~r filings. 

 The substance or condition originating in the activity ofacfjacenf 



spores which has so powerful an effect in orientating the first 

 plane and in determining which cell shall become the 



A 



zoidal cell has no power to cause any chemotropism of the rhizoids 



after they are started. No rhizoid has been found to have its direct- 

 Ti on modified by the presence of other spores adjacent to it. In 

 the absence of any light s$imulus)the rhizoids continue in the direc - 

 tion that they take priginally from the spore. 



