30 
BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 
effects. 1 While various gradations resulted, 2 the experimental pulps 
may be classified in the following three groups : 
Overcooked pulps.- — Severe digestion treatments resulted in "over- 
cooked" pulps, examples of which are seen in Plates II and III. 
The walls of the fibers show a considerable degree of weakness, 
as indicated by their thin transparent appearance and by their 
much twisted and fractured condition. The relative number of 
vessels present in the pulp is low as compared with the normal 
number present in the wood, and the pits and other markings on 
them are only dimly visible. Many of the vessels remaining are 
COOK NO. 
I { 
17 
6 S 4 
COOK NO. 22 
21 20 » IS 17 
A 
A 
— i 
i — 
— < 
> 1 
t (1 <l , 
\ 
1 
B 
S 
c 
i 
Kr- — 
C 
I 
^ 
> II II -»— II = 
D 
D 
— t 
» — 
— II O II II < 
E 
K- ^J 
I 
E 
-4 
►— 
II II II O II 
.10 .20 JO .40 
POUNDS NaOH PER FOUND OF WOOD 
60 10 80 90 100 IK) 120 
MAX. PRESSURE- PDS. PER SCLIN. 
COOK NO. 26 
2 4 6 8 10 12 
DURATION AT MAX. PRESSURE- HOURS 
40 50 60 70 80 90 100 110 
CONCENTRATION NaOH- GRAMS PER LITER 
Fig. 15.— Effects of cooking conditions on pulp fibers. A, abundance of wood vessels; B, ray cells; 
C, fiber bundles, or shives; D, prominence of vessel markings; and E, apparent strength of fiber 
walls. 
ragged and partly disintegrated; and the pulp, for the most part, 
is also characterized by an absence of the comparatively thin-walled, 
delicate ray cells. Fiber bundles also are absent, since these are 
made up of fibers bound together by groups of the brick-shaped ray 
or parenchyma cell. The indistinctness of the vessels and fibers is 
due chiefly to the removal of the ligneous infiltrations of the cell 
walls, in consequence of which the elements developed very little 
color from the particular stain used in making the microscopic 
mounts. 
Well-cooked pulps. — Pulps produced under less severe conditions 
are made up of stronger fibers, such as shown in Plates IV and V. 
1 The remarks following the title of each plate and the discussion in the text are not based on the fields 
shown in the photomicrographs alone. 
2 The photomicrographs, in the order of their sequence, show gradations of severity of cooking. 
