AND INHERITANCE IN PEDIASTRUM. 385 



teristics. There is no question that P. Boryanum may at times, and 

 in the same fashion, develop intercellular spaces, though I have 

 never seen them so symmetrically and strongly developed in this 

 species as in P. asperimi. The production of the general four-lobed 

 outline is, as evidence given below shows, a result of the inherited 

 form of each cell rather than its pressure relations in the colony. 



There is further to be considered a certain suggestion of a want 

 of correlation between the form of the cells and their pressure rela- 

 tions in the colonies of Pediastnmi. Regarding the young cells as 

 equal and rigid globular bodies in one plane, the central cell in a 

 sixteen-celled group would be in contact with and pressed by five 

 cells symmetrically placed about it. Each of the cells of the second 

 series would be in contact with four cells which are not equally 

 spaced about it. The cells of the third series in such a figure 

 would be alternately in contact with one and two cells, correspond- 

 ing to the contacts of the cells of series III. in the actual colony 

 which are alternately in contact with three and four cells (Figs. 

 6, 7). If now the globular cell bodies yield to pressure and flatten 

 upon each other, filling the empty spaces in the group, they will 

 (except the central cell) tend to become oblong and four-cornered 

 like the mature cells of Pediastriim. On the other hand, in the 

 commonest form of the thirty-tzvo-celled colonies the central cell is 

 in contact zuith the six cells of the second series, and each of the six 

 assumed globular bodies would be in contact with five cells not simi- 

 larly placed. In the third series of ten, two such globular cells 

 would be in contact with four each, six would be in contact with 

 three each, and two would be in contact with two each. In the 

 outer series fourteen of the fifteen globular cells would be each in 

 contact with one cell, while one would be in contact with two cells, 

 and yet all these cells in both the sixteen- and thirty-two-celled colo- 

 nies grow into the characteristic four-lobed form with the resulting 

 contact relations found in the mature colony in which in the 

 sixteen-celled colony, for example, the cells of the second series are 

 each in contact with and pressing against six cells and the cells of 

 the outer series are alternately in contact with one and two cells 

 each. The new specific contacts and pressures arising in growth 

 are due to the inherited four-lobed form of the cells, which none 



