DESCRIPTION OF PLATE IV., 



ILLUSTRATING 



MR. ARCHER'S THREE PAPERS— ON ZYGOGONIUM AND MOUGEOTIA 

 (p. 114)— ON ASTERIDIA IN PENIUM DIGITUS (p. 144), AND ON THE 

 CONJUGATION OF TWO SPECIES OF SPIROT^NIA (p. 147). 



Figs. 1-11 x 300 ; Fig. 12 x 400. 



Fig. 1. . . Ordinary sterile filament of Mongeotia lavis, Arch. (= Zygogoninm Iceve 

 ( Kiitz.) ? Unfortunately this figure is faulty in not displaying the 

 central nucleus in each joint. 



,, 2 and 3. Conjugated state of same, showing the zygospores free in the cavity of the 

 transverse tube, the whole contents of the parent cells being absorbed 

 in their formation, and not a central portion only shut off in a special 

 chamber, as in Mesocarpus. 



„ 4. . . A pair of Asteridia shown within the cavity of the cell of an example of 

 Penium digitus, a portion of the original contents of which have become 

 effete and brown coloured. 



,, 5. . . A pair of examples of Spirotcenia condensate/, in juxta-position for the 

 purpose of conjugation; the contents of both individualized into two por- 

 tions, each becoming contracted into an elliptic figure, the spiral ar- 

 rangement of the band of endochrome becoming effaced. 



,, 6. . . The opposite masses of the contents of the original pair of parent-cells 

 now coalesced, and gradually assuming the globular figure and rigid 

 cell- wall shown in next figure. 



„ 7. . . The pair of zygospores having now assumed a globular figure, but not yet 

 showing the honeycomb external decoration. 



,,8. . . The latter more advanced and coating of mucus more densely developed, 

 with a sharply-defined boundary. 



„ 9. . . The pair of zygospores more fully formed, focussed down to the equatorial 

 line, showing the honeycomb structure in side view. 



,, 10. . The same focussed up a little, so as to see partially into the cavities of the 

 honeycomb structure. 



,, 11. . . An empty zygospore, focussed above an equatorial line, showing the 

 mouths of the cells of the honeycomb. 



,, 12. . . The angularly-lobed zygospore of Spirotcenia truncata (Arch.), the four 

 half-cells of the parent pair of cells still appended. 



[Note. — By an unfortunate oversight the above Plate is referred to in the Paper 

 on Asteridia in Penium (p. 144), and on Spirotsenia (p. 147), as Plate VIII. in place of 

 Plate IV.] 



