DESCRIPTION OF PLATES. 



[All the ficrures were drawn with the aid of a Leitz or a Zeiss camera lucida with 

 objectives an<l oculars, as follows: Fig. 1, Leitz No. 1 objective, No. Oconlar; litrs 

 &, b, 7, a, 10, and 12, Leitz ^\ oil-inimersion objective, No. oeular; fi.'. 14 J.eitz V- 

 od-nnmersion objective. No. 3 ocular; figs. In, 17, 18, and 19, Zei.-s 2 mm 1 ;W aper- 

 ture, od-immersion objective. No. 1 Huvghenian ocular; lig.s. 2, .S, 21, 24 '^ti and '^7 

 Zeiss 2 mm. 1.80 aperture, oil-immersion objective. No. G compensating mnl'ar; fi.rs' 

 J2, 2.-J, and 2.0, Zeiss 2 mm. 1.. 30 aperture, oil-immersion objective. No ]2conipeii- 

 sating ocular; tigs. 4, 9, 11, 13, IG, and 20, Zei.ss 2 mm. 1.30 aperture, oll-inmiersion 

 objective. No. Ih compensating ocular.] 



Pl.\te I. RhizopuK nigrirfim. Fig. 1.— Group of sporangiophores Ijearing sporangia, 

 showing how they grow out from the stolon. X 12. Fig. 2.— Longitudi- 

 nal section of young stolon, showing dih:tri))ution of cytoplasm and 

 nuclei. X 750. Fig. 3.— Same, except that the stolon is much older; 

 wall very thick, and nuclei disintegrating. X 750. Fig. 4.— Disinte- 

 grating nuclei from .stolon .shown in tig. 3. X 2,250. Fig. 5.— Youik^ 

 sporangium, showing cytoplasm and nuclei streaming up the sporan^ 

 giophore into the sporangium and out toward the periphery. There are 

 a few crystalloids in tlie center. X 520. Fig. fi.— Si)orangium that has 

 attained nearly its full size. The differentiation between the looser and 

 the den.«er plasms is sharply marked, except at a few places. Just inside 

 the denser plasm is a clear zone of protoplasm that does not take the 

 orange stain, and through this run strands of orange-staining cytoplasm 

 bearing nuclei. X 520. 

 II. lihizopus nigricans. Fig. 7.— Full-sized sporangium, showing layer of vac- 

 uoles nearly formed in the denser i^lasm. The two layers of the wall are 

 here shown. X 520. Fig. 8.— Section cut through sporangium a little 

 to one side of the sporangiophore. The columella cleft is being formed 

 l)y fusion of the vacuoles shown in fig. 7, and by a surface furrow. The 

 spores are also being cut out l)y progressive surface furrows. X 520. 

 Fig. 9.— A small part of the same sporangium as shown in tig. 8, drawn 

 from another section, showing in detail very early cleavage furrows, and 

 structure, size, and distribution of nuclei and vacuoles. X 2,250. 



III. Rhizopm riigricam. Fig. 10.— Cleavage much farther advanced than in 



figs. 8 and 9. Furrows cutting outward from the columella cleft. Sec- 

 tion not cut through sporangiophore. X 520. Fig. 11.— Nuclei from 

 columella of same; a, very close to columella cleft; h, c, and d, nearer the 

 center; a has a normal structure, \<'hile h, c, and d show stages in disin- 

 tegration. X 2,250. Fig. 12.— Sporangium in which the spores are 

 completely formed, rounded up, and surrounded by thin walls. The 

 columella wall is also formed. X 520. Fig. 13.— Nuclei from columella 

 of same; a lies near columella wall and still retains its normal structure; 

 b lies near it but is beginning to disintegrate; c and d lie near the center 

 and are reduced to homogeneous angular masses. X 2,250. Fig. 14.— 

 Ripe spores in their living condition, showing variations in size and 

 ridges on walls. X 950. 



IV. Fhycomyces nitens. Fig. 15.— Young sporangium, showing cytoplasm nuclei 



and vacuoles streaming up the sporangiophore and out toward the periph- 

 ery of the sporangium. Vacuoles in the denser protoplasm have a visi- 

 ble content. X 550. Fig. 16.— Small part ©f young sporangium very 

 highly magnified, showing early stage in the formation of the visible 



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