84 • F. McAllister 
of minute, flattened spindle- or scale-like bodies forming the so-called 
' ' pyrenoid ' ' (figures 1,2, and 3) . An examination of a great variety of 
cells in various stages of activity shows definitely that there is never 
a homogeneous unsegmented center about which starch grains are 
formed as is the case with the pyrenoids of the green algae. Wherever 
a pyrenoid is to be seen it always appears as a group of from 25 to 300 
very minute bodies rather than a single, large, spherical body. This 
group of bodies is often so compact as to appear practically homo- 
geneous when viewed with a four millimeter objective although fre- 
quently, when they are not crowded, the bodies can be seen with a 
sixteen millimeter objective. It seems nevertheless possible that with 
poor fixation and staining the individual bodies might at times be 
unrecognizable even with an oil immersion objective. 
These pyrenoid bodies, as I shall call them in the following pages^ 
stain red or reddish with Flemming's triple stain, the brilliancy of the 
stain depending apparently upon the activity of the cell and plastid. 
In cells which are semi-dormant where growth is very slow and the 
pyrenoid bodies are closely crowded, they stain a dull reddish color. 
When loosely aggregated, as they are usually when photosynthesis is 
very active, they appear as flattened, scale-like bodies which stain 
a brilliant red. Starch grains which nearly always surround them 
under these conditions always take the violet stain. With Millon's 
reagent the central aggregation of bodies stains orange and with 
nitric acid the characteristic xanthoproteic reaction is obtained, — the 
surrounding starch grains in both cases remaining colorless. These 
reactions indicate as definitely as our present microchemical tests 
permit the protein nature of the pyrenoid bodies. 
As has been suggested above, considerable difference exists in the 
degree of aggregation of the bodies which make up the pyrenoid. 
Those in the cells which contain little or no starch, or in other words, 
in which photosynthesis is not active, show always a compact mass of 
pyrenoid bodies. Figure 6 shows such an aggregation in a small cell 
near the growing point. The deeply lying cells of the mature thallus 
usually have such dense aggregations (figures i and 19). It is of interest 
in this connection to note that the peripheral cells, even on the lower 
surface of the thallus, always show much more active. photosynthesis 
than those submerged in the thallus, a condition which is without 
doubt due to insufficient aeration of the interior regions. 
In certain thalli, which are apparently in a dormant condition^ 
