AND INHERITANCE IN PEDIASTRUM. 379 



the most abundant species as I have found them, next to P. Borya- 

 num Kg., is P. aspertim (Figs. 5 and 6). P. aspermn has been 

 regarded by many as a form of P. Boryanum. Whether or not it 

 is to be considered a good species, the forms as I have found them 

 reproduce the type so far as cell form, involving as it does the char- 

 acteristic intercellular spaces, is concerned with a high degree of 

 constancy. I have never seen a colony with the asperum cell form 

 produced from a Boryanum parent nor a colony without intercellu- 

 lar spaces from an asperum, parent. 



I have been able to study and photograph P. asperum in all 

 stages of the vegetative growth and reproduction of the colonies 

 and it may well serve to illustrate the two-spined forms with well- 

 developed intercellular spaces and cells similar throughout the col- 

 ony in contrast with P. Boryanum with intercellular spaces small 

 or wanting and interior cells only slightly or even not at all two- 

 spined, as I have already described it ('16). 



Arrangement of the Cells and Intercellular Spaces in the 

 Sixteen-Celled Colonies of P. asperum. 



The spatial interrelations of the cells are essentially the same in 

 the typical sixteen-celled colony of P. asperum as in the typical 

 sixteen-celled colony of P. Boryanum, as I have described it else- 

 where ('16), and as it has long been known in the literature. But 

 in P. asperum the cells are all very much alike in form, the interior 

 cells having only slightly shorter lobes than those on the periphery 

 of the colony. We may consider first the sixteen-celled colony, 

 which is perhaps the most common, though 8-, 32-, 64- and 128- 

 celled colonies are found. I shall leave the colonies with 32, 64, 

 128, etc., cells without discussion at this time, since certain further 

 elements in morphogenesis implied in the larger number of units 

 are involved which I shall take up in a later paper. A common ar- 

 rangement in the thirty-two-celled colony is 1+6+10-I-15, as 

 noted by Braun ('55). The presence of six cells in series IL of 

 the thirty-two-celled colony as compared with the five in series II. 

 of the sixteen-celled colony introduces quite fundamentally differ- 

 ent relations between the oblong four-lobed form of the cells and 

 the natural surface tension factors in such groups. 



