•40 FORMATION OF SPOEES OF RHIZOPUS AND PHYCOMYCES. 



content of the vacuole; also two much smaller vacuoles with no such 

 contents; nuclei in resting condition. X 2,250. Fig. 17. — Portion of 

 cross section of sporangium at a somewhat later stage than fig. 15, show- 

 ing distribution of protoplasm into an outer dense layer, an interior 

 region of very loose protoplasm containing empty vacuoles and no nuclei, 

 and between these two a layer of intermediate density. X 550. Fig. 

 18. — Part of longitudinal section of sporangium, showing laj'er of vacu- 

 oles forming in denser protoplasm where the columella is to be cut out. 

 X 550. 

 Plate V. Phycomyces nitens. Fig. 19. — Layer of vacuoles in the denser plasm, flatten- 

 ing out toward each other to form the columella cleft by their fusion. The 

 contents flatten out also, taking the shape of the vacuoles. X 550. Fig. 

 20. — Small part of section very highly magnified, showing three vacuoles 

 in contact, separated only by their membranes; also three very small 

 empty vacuoles and six nuclei in resting condition. X 2,250. Fig. 21. — 

 Spore plasm Vjeing cut up into spores by vacuoles becoming angular, and 

 the angles cutting through the protoplasm as furrows; cytoplasm in front 

 of furrows undifferentiated; nuclei in a resting condition. The contents 

 of the vacuoles extend out into the furrows and fuse as the furrows fuse, 

 to form the intersporal substance. X 750. Fig. 22. — Furrows cutting 

 outward into the spore plasm from the columella cleft; cyt< plasm in 

 front of furrows undifferentiated. X 1,500. Fig. 23. — Furrows from the 

 vacuoles cutting out to the plasma-membrane at the periphery of the 

 sporangium. X 1,500. Fig. 24. — Xearly ripe spores containing resting 

 nuclei and empty vacuoles, and embedded in intersporal slime. X 750. 

 Fig. 25. — Living, ripe spores; walls smooth; cr, very large; 6, average size; 

 c, very small. X 1,500. Fig. 26. — Very large peculiar-shaped spores; 

 e, probably due to arrested cleavage. X 750. Fig. 27. — Very large, 

 irregular-shaped spore due to arrested cleavage. X 750. 

 VI. Filoboluscrystallimis. (Diagrammatic and much simplified.) Fig. 28. — One- 

 half of longitudinal section of sporangium just before the cutting out of 

 the columella. The arrows indicate lines of contraction of the cytoplasm 

 to form the columella cleft. Green arrows indicate points where the con- 

 traction is just beginning and red arrows points where the contraction is at 

 its maximum strength; dotted black lines represent planes where cleavage 

 is to take place. Fig. 29. — Same, but somewhat older stage; vacuoles 

 flattened to fill the spaces where the cytoplasm has been pulled away; 

 also surface furrow at the base of the sporangium. Blue arrows indicate 

 points where contraction has passed its maximum strength. Fig. 30. — 

 Columella cleft completed, spore formation just ready to begin. Fig. 31. — 

 Vacuoles in the spore-plasm becoming angular, and furrows cutting 

 inward from the periphery and outward from the columella cleft, due to 

 the cytoplasm pulling away at these points. Fig. 32. — Synchitriiim decip- 

 iens. (After Harper.) Two cleavage furrows cutting into the sporan- 

 gium. These are slightly open at the inner extremity where the cyto- 

 plasm is contracting, but closed nearer the periphery of the sporangium 

 where contraction has ceased. Fig. 33. — FuUgo varians. (After Harper. ) 

 Two furrows cutting into the spore plasm; furrows slightly open through- 

 out their entire extent. Fig. 34. — Squid. (After Watase. ) Surface 

 view of egg, showing cleavage furrows cutting into the cytoplasm between 

 the nuclei; furrows very narrow at the extremities. 



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