20 FORMATIOI^ OF SPORES OF RHIZOPUS AND PHYCOMYCES. 



spores of the Saprolegniete. It is not, however, surprising that with 

 the technique used in those da^^s he should fail to see that there was 

 still a distinct boundary between the closel}' packed spores. 



When the period of turgor relaxes a little the two surfaces generally 

 separate slightly, but at irregular intervals points are often found 

 where they still adhere, forming tiny conical projections, whose apices 

 are for a short time in contact. 



In the behavior of these two protoplasmic surfaces we have consid- 

 erable additional evidence for the existence of a definite plasma-mem- 

 brane. 



Even before the cutting out of the columella takes place the nuclei 

 of the looser protoplasm begin to disintegrate. In very young spo- 

 rangia all the nuclei have the same normal structure, but in the one 

 shown in PL I, fig. 6, for example, they are clearly sufl^ering disinte- 

 gration in the center of what is to become the columella-plasm, though 

 out near the denser plasm they retain their characteristic structure, 

 often until the spores are nearly ripe. (PI. Ill, fig. 13, a.) 



It might be suggested that the nuclei in the center of the sporangium 

 are not well fixed, but these sporangia are so small and thin-walled 

 that I can not believe, with all the c3^toplasm and the greater part of 

 the nuciei having a perfectl}^ normal strvicture, that the difference in 

 appearance of these nuclei is to be attributed to poor fixation, espe- 

 cially as it is essentially the same for all the best fixing fluids used. 



The first sign of disintegration is the appearance of a red-staining 

 mass on one side. As the process goes on, the whole nucleus comes 

 to appear as a slightly shrunken, homogeneous mass, often irregular 

 in shape, and staining the same shade of red as the cr3\stalloids. It 

 might be argued that these red-staining bodies are cr3^stalloids whose 

 substance is being dissolved, but 1 have found very good evidence that 

 such is not the case. As shown in PI. Ill, figs. 11 and 13, there are all 

 stages of disintegration between the almost perfect nuclei and the most 

 shrunken and angular ones. On the other hand, all the crystalloids in 

 these sporangia, so far as could be observed, are perfect in shape, 

 none showing notches or marks of corrosion, such as we should expect 

 to find if they were being dissolved. Furthermore, the crystalloids 

 seem to be forming rather than dissolving, judging from their greater 

 number and size in the older sporangia. 



In PI. Ill, figs. 11 and 13, a represents a nucleus with normal 

 structure lying just inward from the denser plasm, while 5, t\ and d 

 lie nearer the center and are breaking down. In no sporangia as old 

 as that shown in PI. I, fig. 6, have I found nuclei in or near the center 

 of the looser plasm in which nuclear membrane, chromatin, and nucle- 

 olus could be distinguished. These nuclei do not entirel}"^ disappear 

 during the life of the plant, nor would it be at all accurate to say, as 

 Leger has done, that the}^ are ''reduced to a nucleole." 



