264 



MONOGRAPH OF THE LABOULBENIACE^E. 



Family LABOULBENlACEiE Petbitsoh. 



DIMORPHOMYCES Thaxter. Plate V, figs. 1-16. 



Proc. Am. Acad. Arts and Sci., Vol. XXVIII, p. 157. 



Dioecious. Male individual consisting of four superposed cells, the two distal ones sterile, 

 the sub-basal producing a compound antheridium, the six antheridial cells of which are arranged 

 in two antero-posterior rows and discharge into a common cavity lying above them, from which 

 the antherozoids escape through a prominent tubular neck. 



Female individual consisting of four superposed cells, the two distal ones sterile, the sub-basal 

 cell giving rise to two or more perithecia and sterile appendages which alternate with one another 

 on either side, forming a transverse series. Trichogyne short, radiately branched. Spores once 

 septate. 



The material available for the illustration of this genus, although abundant, includes, unfor- 

 tunately, no young individuals in which the first stages in the development of the primary peri- 

 thecia are shown. Owing to the small size of the plant and the indistinctness of its septa, it 

 has been difficult to determine with certainty the exact relation which the perithecia and sterile 

 appendages bear to the receptacle. While in most cases the latter has seemed to consist of 

 three superposed cells, as in fig. 1 or 5, in a few specimens I have thought that there was an indi- 

 cation of the presence of septa as is indicated in fig. 4. If the first of these alternatives proves 

 to be correct, the portions of the receptacle which bear the appendages and perithecia must be 

 considered as wing-like outgrowths from the basal cell ; while in the second instance they would 

 originate from a sub-basal cell. Although in no other genus, with the exception of Amor- 

 phomyces, is anything approaching a similar condition found, I am inclined to think that the 

 first-mentioned alternative is the correct one. 



In form and development the species of Dimorphomyces are very peculiar. There is a gen- 

 eral triangular outline to the portion below the sterile cells of the receptacle, a tendency to a 

 posterior convexity and anterior concavity ; and in both species the first organs to be developed 

 are a pair of primary perithecia symmetrically placed and followed immediately by a sterile 

 appendage placed externally on either side. In many individuals there seems to be no further 

 development (fig. 3) ; but very commonly two or four secondary perithecia are formed, alter- 

 nating with as many sterile appendages. The process by which these organs are formed is unlike 

 any corresponding process in other genera. Assuming that my observations are correct in de- 

 riving them from the sub-basal cell of the receptacle, the first step in their formation would 

 consist in the production of two anterior projections from this cell symmetrically placed on either 

 side of the median line. The tip of each projection is cut off, and the cell thus separated de- 

 velops upward into a perithecium. Meanwhile a lateral proliferation takes place below this 



