A STUDY OF PLASTIDS AND MITOCHONDRIA 
223 
the plerome, a marked change occurs. The mitochondria now appear as 
elongated, thread-like bodies, seeming to have arisen from the spherical 
and ovoid forms by a process of lengthening and thinning. Of these elon- 
gated forms, many appear hooked, or in some cases vacuolate, at the ends. 
Mingled with these thread-like structures are others which appear circular, 
as if a thread had formed a ring, or possibly a globular form had changed in 
appeamnce so that it resembles a hollow sphere. At times, chains of small 
granules are seen, probably due to the breaking up of a filament. Figure i 
shows the large number and greatly varied shapes of the mitochondria in 
this region. 
Passing outward from the region of elongated cells in the plerome and 
entering the periblem, the cells are found crowded with mitochondria, 
mostly spherical in shape. It appears as if the mitochondria do not, in 
general, elongate in this region, though they increase in size, approximately 
to the same extent in all directions. As will be shown later, these enlarged 
bodies of the periblem are in reality not mitochondria, but plastids, though 
they stain in exactly the same manner with the haematoxylin. Whether 
there are any plastids present in the plerome region as well, I am not as yet 
prepared to say. Figure 2 shows a cell from the periblem in mitosis, drawn 
to the same scale as figure i, namely, nine hundred diameters. Figure 3 
shows a similar cell enlarged to twice the size. 
As may be seen from these drawings, the mitotic figure is shown very 
much as it appears in the usual method of fixation, with the exceptions to 
be noted. The spindle fibers are but faintly shown, if visible at all, although 
the general outline of the spindle appears as it normally does. The chro- 
mosomes are rather attenuated, though they sometimes show a shadowy 
outline of surrounding material, as if only the central part of their structure 
had been stained. The difference between this method of fixation and those 
methods designed primarily for showing nuclear structure, is much more 
marked in the resting cell. Here the nucleus appears, in general, more 
uniformly granular and less reticulate than it does in preparations fixed, 
say, in Flemming's strong fluid. The nucleole also is different, appearing 
much larger than we are accustomed to see it in fixed material. In short, 
the mitochondrial methods of fixation do not seem to alter the appearance 
of the protoplast so much as do the usual types of fixation, since with the 
mitchondrial methods the structure appears very much as it is described by 
Lewis and Lewis ('15) and by Lewis and Robertson ('16), in their obser- 
vations upon living tissue cells. 
The root-tips from which the above described preparations were made 
were grown in the laboratory during the coldest part of the winter and not 
under constant temperature conditions. To this I attribute the difference 
between the granular content of the cytoplasm in this material and in the 
preparations next to be described. 
Root-tips of the same variety of corn, grown later in the season and under 
