Hydrodictyon utriculatum . 627 
in Fig. 1, is seen to have in a general way, but quite clearly, 
orientation about the pyrenoid as a centre. The concentric 
arrangement will be especially noted in Fig. 5. This arrange- 
ment seems to point clearly to the common origin of all 
the starch-grains from the pyrenoid in the manner described 
above. 
The failure on the part of former observers to trace the 
origin of all the starch to the pyrenoid is due, as I have 
previously indicated, to the lack of material taken in a con- 
dition of active starch-development, coupled with methods of 
treatment inadequate to bring out the stages in the genesis 
of the individual grains. That various observers have drawn 
their conclusions from a study of isolated stages in starch- 
development is shown by the conflicting statements as to the 
form of the pyrenoid itself. Schmitz maintained that it is 
a spherical body, a conclusion doubtless drawn from a study 
of resting pyrenoids as described above. Meyer probably 
saw a single stage in starch-formation and was led to insist 
upon the angular form of the pyrenoid. It is even possible 
that the star-shaped pyrenoid described by Chmielewski was 
simply a condition similar to that shown in Fig. 4. 
The size of the pyrenoids at the time they are forming 
or about to form starch is very variable. While in many 
cases the pyrenoids are of approximately the same size in 
any one cell during active starch-formation (Fig. 1), in many 
others there is a very wide variation. Two pyrenoids repre- 
senting almost extremes in size are frequently found lying 
side by side in the same part of the cell, either or both of 
which may show the beginning of starch- formation (Fig. 21). 
Whether these represent pyrenoids of different ages with 
independent genetic histories, or whether they are sister organs 
formed as the result of the division of a pre-existing pyrenoid, 
is an important question, as yet unsettled. There is abundant 
evidence that the development of the starch may take place 
in such a way as to completely divide the pyrenoid into two 
parts. This is most often brought about by the equatorial 
region of the pyrenoid being transformed into starch in such 
T t 
