AND INHERITANCE IN PEDIASTRUM. 389 



sections stages showing the cleavage of numerous segments of the 

 sporeplasm and my photographs show the first division, four-cell 

 stage, etc. Smith's figures show .clearly that the cells divide by 

 furrows and that regular karyokinetic figures appear in nuclear 

 division. The swarmspore is uninucleated and the sporeplasm be- 

 comes multinucleated before cell division begins. 



When the colony is to reproduce itself the cells become extremely 

 plump and to some extent lose their deeply four-lobed form (Fig. 

 8). The spinous projections tend to be drawn in perhaps, though 

 they do not entirely disappear in any of the species. This is well 

 shown in figures of F. aspermn, 8, 9, and 10, and at a later stage 

 when cleavage is well along in Figs. 11, 12 and 14. These forms 

 would hardly be recognized as belonging to P. asperum if it were 

 not possible to find all conceivable intermediate forms between these 

 very turgid types and the immature colonies with slenderly lobed 

 cells, such as are shown in Fig. 6. In such species as P. clathratttm 

 (Fig. 3) with its very deep sinuses and slender-branched cells it is 

 plain that the four-pointed cell form maintains itself strongly even 

 against the effects of increase of turgor. 



As Askenasy ('88) noted, the nuclei are readily recognizable at 

 this stage. Askenasy mentions, but without figures, that the cell 

 division proceeds by a series of successive bipartitions. Figs. 10, a 

 and h, show the mother cell dividing into two. Cells c, d, e in the 

 same figure show at least the beginnings of the four-cell stages. It 

 is very difficult owing to the density of the cell contents at these 

 stages to bring out the cleavage clearly in photographs, though the 

 furrows are easily visible on focusing. The divisions apparently 

 occur by constriction furrows from the plasma membrane inward 

 as described by Smith ('16), as noted, and by Timberlake ('02) for 

 Hydrodictyon. There is no indication of the formation of cell 

 plates, so far as the appearance of the living material is concerned. 

 That we really have constriction furrows forming here and not 

 merely lines of simultaneous cleavage as claimed by Swingle ('97) 

 for Stypocaulon and by various authors for a number of fungi 

 (Baum, '00, Kusano, '09, Barrett, '12, Griggs, '12) is suggested by 



PROC. AMER. PHIL. SOC, VOL. LVII, aa, AUG. ip, 1918. 



