644 Journal of Agricultural Research voi. xv, no. 12 



the disappearance of the nuclear membrane the nucleolus is cast out 

 (PI. 58, N), after which it migrates off to some distance from the chromatin 

 mass. A true spindle is then formed at the two ends of which are located 

 the centrosomes (PI. 58, O, P). The original centrosome was not seen to 

 divide, but the conformation of the spindle in some early stages suggests 

 the division of the centrosome to form two, which move apart and 

 become oriented as the opposite poles of the spindle. The chromatin 

 now appears in deeply stained sections as a convoluted dark mass at the 

 middle of the spindle (PI. 58, O). With better differentiation this mass 

 resolves itself into a jumble of more or less rounded units, the chromo- 

 somes (PI. 58, P). This stage corresponds to the equatorial plate stage 

 of the metaphase. The chromosomes are now seen to separate and move 

 toward the poles (PI. 58, Q-S) ; they seem to flow along the outer surface 

 of the spindle rather than to be drawn definitely apart by attraction 

 fibers. Unless very carefully differentiated, the chromatin at this stage 

 may appear to be a single knotted thread reaching from pole to pole. 

 The chromosomes, however, do not fuse into one mass, but, as can be 

 seen in favorable preparations, remain as separate units (PI. 58, R). As 

 they approach the poles the chromosomes apparently arrange themselves 

 into two groups (PI. 58, T) for each pole. The division of the centro- 

 somes before the daughter nuclei are reorganized may explain the locus 

 of the two groups, as suggested by Olive {41). At this late stage of 

 anaphase the whole figure may resemble the silhouette dumbbell figures 

 by earlier investigators of the subject. The two groups at each pole now 

 become condensed to two deeply staining masses (PI. 58, U). Fibrous 

 connections between the daughter groups may still remain visible. The 

 cast-out nucleolus has persisted in the cytoplasm up to this time, slowly 

 becoming less dense and often decreasing in size, while the process 

 described above has been taking place, but as the last spindle fibers 

 disappear and the daughter nuclei begin to become reorganized it fades 

 away, completely absorbed by the cytoplasm. The companion nucleus 

 of the dikaryon, having divided simultaneously with the one described, 

 has by this time given rise to two other daughter nuclei. The four reor- 

 ganizing nuclei now move apart, two and two, the sister nuclei separating 

 and moving in opposite directions. A wall now forms (PI. 58, V, a), 

 separating the upper pair from the lower, forming the seciospore initial 

 and, below it, a new basal cell (PI. 58, M), potentially equivalent to the 

 primary basal cell. 



STEPS IN FORMATION OF ^CIOSPORE CHAIN 



Division of the dikaryon in the seciospore initial follows the same 

 process as that in the basal cell (PI. 58, W, M, h, X). The wall which 

 forms between the two pairs of nuclei divides the original initial cell into 

 two parts, an upper cell which is the seciospore and a lower, which is the 

 intercalary cell (PI. 58, Y, d, c). Repeated division of ihe basal cell and 



