414 HARPER— ORGANIZATION, REPRODUCTION 



How much significance can be attached to the degree of agree- 

 ment obtained by the two methods used in obtaining the norms of 

 all these fluctuating elements can only be determined by more ex- 

 tensive statistical studies both of especially symmetrical single colo- 

 nies and extensive series of colonies chosen only on the basis of 

 their having a similar arrangement of their cells. The tendency to 

 equality shown in the values of the corresponding angles both for 

 the intersection of the walls and for the spaces occupied by the 

 entire cells ceftainly suggests that the structure of the colony tends 

 to be a least-surface configuration with all angles of intersection of 

 the cell walls equal to 120° and all the cells subtending equal angles 

 about the center of the colony, this tendency being in every case 

 limited, however, by the inherited form of the cells and the acci- 

 dents of environment. 



The results of my measurements of the homologous angles in 

 the colonies of Pediastrum are in agreement with Rhumbler's ('02) 

 results obtained by measuring the homologous marginal angles of 

 various Foraminifera and confirm still further the conception of 

 the semi-liquid nature of plant and animal protoplasm. Rhumbler 

 uses these results primarily as evidence on this point. The fact 

 that only homologous angles tend to be equal leads him at once, 

 however, to emphasize the heterogeneity in structure of the proto- 

 plasm resulting in an anomogenous consistency and anomogenous 

 tensions in different regions of the cell. The cell of Pediastrum 

 with its inherited four-lobed form operating always with surface 

 tension in determining the value of any given cell angle is also a 

 notably anomogenous system, as compared with a simple fluid drop- 

 let. In the morphogenesis of the colony it is obvious that this 

 anomogeneity is quite as important a factor as is the principle of 

 surface tension. It is in the indisputable evidence from both 

 Rhumbler's material and my own of the interplay of capillarity, 

 protoplasmic anomogeneity, and especially of the principle of binary 

 fission that we get a basis for interpreting the complexity of the 

 form elements with which we are confronted even in such simple 

 organisms as the Foraminifera and coenobic alg?e. The least-sur- 

 face configuration comes to expression in Pediastrum in so far as 

 is consistent with the inherited cell form and consistency and with 



