634 Timber lake. — Starch-Formation in 
strongly negatived. I am inclined to the view that the 
pyrenoid is an active body, differentiated in the chlorophyll- 
bearing cytoplasm, which in co-operation with the latter acts 
as the base of the process of starch-formation. In just what 
the co-operation consists must remain to be determined by 
future investigation. 
If we compare the method of starch-formation in Hydro - 
dictyon as described above with starch-formation in chromato- 
phores without pyrenoids, there is little to suggest a parallel, 
and the relations of the two must be regarded as uncertain 
for the present. 
Madison, Wis., May, 1901. 
EXPLANATION OF FIGURES IN PLATE XXXIV. 
Illustrating Mr. Timberlake’s paper on Starch-Formation in Hydrodictyon. 
All figures were drawn with the aid of the Abb£ camera lucida , and with the 
Zeiss apochromatic objective 2 mm., num. ap. 1*30, and compensation oculars 
4, 12, and 18. 
Fig. 1. Part of surface-section of cell, showing condition of rapid starch 
formation ; P. pyrenoid, S. starch, x 1 500. 
Figs. 2, 3. Details of starch-formation in single pyrenoids. x 2250. 
Fig. 4. Shows peculiar angular form of pyrenoid. x 2250. 
Fig. 5. PyrJ*noid surrounded by distinctly concentrically arranged layers of 
starch, x 2250. 
Fig. 6. Starch-formation, where solution of starch is going on nearly as rapidly 
as its formation. 
Fig. 7. Young cell, showing two small pyrenoids in which no starch is forming, 
and a larger one in which a single grain of starch is being formed. 
Fig. 8. Same as above. 
Fig. 9 a. Cell, showing pyrenoid without starch, and surrounded by a colourless, 
clearly bounded area. Pyrenoid itself shows but a faint colour, x 2250. 
Fig. 9 b. Starch-forming in pyrenoid with colourless region as before. Small 
pyrenoid lying against nucleus, x 2250. 
Figs. 10-18. Different phases of starch-formation resulting in the division of the 
pyrenoid. For explanations see text, x 2250. 
Figs. 19, 20. Showing disappearance of pyrenoid without the starch being 
entirely dissolved, x 2250. 
