Hydrodictyon utriculatum . 629 
of Hydrodictyo?i disappear prior to the formation of the 
swarm-spores or gametes has been known since Braun’s 
classic researches on Rejuvenescence in Nature. This of 
course necessitates an origin de novo in the young cells. 
Hence division cannot at least be considered the only means 
for the multiplication of pyrenoids. 
The steps in the disappearance of the pyrenoids and usually 
of the starch prior to cleavage are worthy of attention, and 
for the starch may be taken as typical for the process of 
starch-solution in the plant. Generally the first starch to dis- 
appear is, as might be expected, that farthest from the pyre- 
noids. The starch-grains seem to be dissolved uniformly over 
the surface instead of in furrows and by irregular corrosions 
as is often observed in the storage-starch of the higher 
plants. Very often a stage is seen where there remains but 
a single layer of starch around the pyrenoid, while the pyre- 
noid itself shows no indication of further starch-formation, but 
has the homogeneous structure and spherical form of the 
typical resting pyrenoid (Fig. 21 : large pyrenoid). This stage 
is also often met with in cells that give no other indica- 
tions of reproductive activity. It probably represents, as 
previously suggested, a quiescent condition of the cell so far 
as starch-formation is concerned, and the frequency of its 
appearance serves to explain Schmitz’s account of the pyrenoid 
as a spherical body surrounded by a single layer of starch. 
Such stages must be carefully distinguished from that repre- 
sented in Fig. 6, where there is manifestly development of 
starch taking place, but where also the solution of the starch 
seems to wellnigh keep pace with its formation so that there 
is but little more than a single layer of starch around the 
pyrenoid. Let the process of starch-formation cease in such 
a condition as this last, and we can very readily imagine the 
whole structure passing over into such a resting-stage as that 
shown in Fig. 21. As the solution of starch continues, the 
pyrenoid itself generally becomes smaller, although the starch 
is usually all dissolved before the pyrenoid has entirely dis- 
appeared (Figs. 22-24). Still, it is not necessary that either 
T t 2 
