AND INHERITANCE IN PEDIASTRUM. 383 



of P. Boryanum. They all show a reentering angle on their periph- 

 eral sides. In P. asperiim this tendency to the four-lobed form has 

 come more fully to expression, overcoming to quite a degree the 

 adhesion of the cell surfaces so that each cell may assume the form 

 to which its inherited tendencies predispose it. The possible origin 

 of this tendency in the intercellular relations of such groups of cells, 

 I shall discuss later. 



In form these intercellular spaces vary from youth to the 

 adult reproductive condition, as will be noted later in discussing 

 reproduction. They also show some degree of variation in differ- 

 ent individuals of apparently the same stage of development. In 

 their curved outlines they express very fully the tensions existing 

 in the protoplasm of the cells and the contact relations of the cells 

 in the colony. In colonies with atypical cell arrangement, they may 

 become highly varied in different regions, expressing fully the dif- 

 ferent and irregular tensions set up in such abnormal or subnormal 

 groupings (Figs. 26-28). 



In number, form and position these intercellular spaces form 

 two series, four between the central cell and series II. and ten be- 

 tween series II. and III., the outer series. Of the four intercellular 

 spaces of the inner series two, a and c (text-fig. 7) lie on the axis 

 of the colony, and the other two, h and e, are symmetrically placed to 

 the right and left. These four spaces are of three forms and sizes, a, 

 the largest, is broadly triangular to shield-shaped (Figs. 5, 6) ; c, the 

 second in size, is roughly an asymmetrical ellipsoid with its greater 

 convexity toward the central cell, and h and e are still smaller and 

 more or less symmetrical ellipsoids with pointed poles, somewhat 

 lemon-shaped. 



The outer series consists of five larger, ovoid to shield-shaped 

 spaces, i, k, 0, t and q, and alternating with them five smaller 

 spaces, f, h, j, I and p. One of the larger spaces, q, and one of the 

 smaller, /, are bisected by the axis of the colony. The remaining 

 four of the larger group may be regarded as forming two pairs, a 

 pair, i and k, symmetrically placed to the right and left of the axis, 

 nearer the m pole of the colony, and nearer together than and t, 

 the similarly placed pair toward the n pole. The remaining four 



