3-1 FORMATION OF SPORES OF RHIZOPUS AND PHYCOMYCES. 



Pfeflfer (1890) confirms the conclusions of De Vries and "Went that 

 the vacuole wall is an osmotic membrane very much like the haut- 

 schicht. and that it reproduces itself by division. He is able to form 

 new vacuoles in plasmodia. however, by introducing very small parti- 

 cles of asparagin, and finds these to agree in all essential particulars 

 with normally produced vacuoles. He also holds that b}' extensive 

 vacuolization nearly all of the cytoplasm may be changed to "'plasma- 

 haut" (vacuole wall and hautschicht). Pfefl'er, seems, however, 

 inclined to regard both the vacuole wall and the hautschicht as the 

 result of surface tension, and a precipitation of the surface of the 

 cytoplasm by contact witli water. 



Biitschli (1892) also refuses to accept the view that the vacuole is 

 bounded by a definite, permanent wall, and would, with Pfetfer, refer 

 it to surface tension between the watery liquid of the vacuole and the 

 viscid, semiliquid protoplasm; or. at most, he regards this boundary 

 as only a precipitation membrane formed by the action of the vacuo- 

 lar contents on the adjacent protoplasm. 



In the part played b}" the vacuoles in the formation of the spores in 

 the Mucorineaj we have additional evidence that the vacuolar membrane 

 is a more definite structure than Biitschli regards it. The vacuolar 

 membrane so clearly is able at times to perform the functions of the 

 plasma-membrane that the structure and composition of the two seem 

 identical. 



The exact composition of the stainable substance in the vacuoles of 

 Phycomyces is not easy to determine. In living sporangia crushed 

 under a cover-glass it is easy to see the vacuoles more or less isolated 

 from the cj'toplasm, but no contents can be seen at o-wj stage of 

 development. Neither can the intersporal substance be seen in spo- 

 rangia where cleavage is only partially complete. In older sporangia, 

 however, this is clearh' visible. This would suggest that this sub- 

 stance is in solution or very transparent in living sporangia and is 

 precipitated in the process of dehydrating or clearing — probably by 

 the alcohol. It appears in sections of old sporangia even before stain- 

 ing, no matter what fixing fluid is used. It is not readih' soluble in 

 water, as maj' be seen from the fact that it is visible in sections that 

 have been soaked several hours in water. 



In seeds, Wakker (1888) found that the aleurone grains inside the 

 vacuoles begin as very minute, dense bodies, much smaller than the 

 vacuoles themselves, afterwards increasing in size till the vacuoles are 

 nearly or quite filled hy them. As I have already- pointed out, how- 

 ever, the contents of the vacuoles of Phycomyces are at the moment 

 the}' first become \isible quite as large in proportion to the size of the 

 vacuole as when the}' become older. The substance seems to be evenly 

 distributed in the cell sap of the vacuole, simply increasing in density 

 as the sporangium grows older. There can be little doubt that it is a 



