AND INHERITANCE IN PEDIASTRUM. 399 



to the large and small intercellular spaces, that is, the regions of 

 contact of three and two cells respectively about the points d, d^, d', 

 etc., as I did in the case of P. Boryanum. Such diflferences if they 

 are present in P. aspcrunt are within the limits of error with the 

 methods of measurement I have so far been able to employ. 



The deviations from 120° range from 117° to 123°. The method 

 is not, however, exact and the successive series of measurements 

 from which the averages in the table are derived have little value 

 further than to show plainly enough that the fluctuations here are in 

 most cases relatively slight, and that they appear to range rather 

 equally about 120° for all the cells in the colony. 



I have some slight evidence that the inner angle a of the three at 

 the points r/^_, g-, etc., and d, d'^, d~, etc., averages a little larger than 

 the other two angles, b and c, but the evidence is by no means ade- 

 quate on this point and I reserve the data till some further method 

 of testing the questions involved has been devised. It is obvious 

 enough that the fluctuations in the values of these angles of inter- 

 section are much less in P. aspcniiii than in P. Boryanum and this 

 fact is evidently correlated directly with the formation of the large 

 intercellular spaces in P. asperum, which permit a curving of the 

 lobes and a general distortion of the whole cell body which results 

 in a more perfect equilibrium between the surface forces at the 

 points of contact of the cells. 



The relative degree of conformity to type in a series of the 

 sixteen-celled colonies of P. asperum can be better studied by com- 

 paring the angles subtended by each cell about the center of the col- 

 ony. These angles can be measured with more accuracy, and, while 

 they show considerable individual variations, the averages of the 

 rather small numbers obtained show considerable constancy. We 

 may take first a series of fourteen colonies whose cells are arranged 

 in the most common order, namely, one in the center with five 

 around this in the so-called second series and ten in the third or 

 outer series. 



It is plain from the table that the bases of the cells of both the 

 second and third series tend to be equal and regarded as arcs of a 

 circle about the center of the colony r (Fig. 7) subtend approxi- 

 mately equal angles. The cells of series II. occupy on the average 



