422 BOTANICAL GAZETTE [NOVEMBER 
and 4106.96 gm., 32.06 and 38 gm. per mm.?, or 3,104 and 3.678 atmospheres 
respectively. 
4. The hard seed and fruit coats of Corylus and Pinus are greatly weak- 
ened at the dehiscent line merely by water absorption. The breaking re- 
sistance offered by the soaked coats in these forms is generally one-half to 
one-sixth that offered by the dry coat. This weakening is not due to the dis- 
solution of materials from the dehiscent line, for the old breaking strength is 
cellulose is present, as in Juglans. In Pinus, if rings of the coat were buried 
in soil for a period considerably exceeding germination time, the dehiscent 
zone was considerably weakened by soil agents. In these experiments, how- 
ever, the agents can attack the dehiscent zone from every side. Water 
absorption also greatly lowers the breaking strength of brittle coats like 
Ricinus, as well as leathery or skinlike coats, as in Vicia Faba. It seems that 
the breaking strength of a great number of organic substances (Laminaria 
thallus, filter and parchment paper, etc.) falls greatly with water absorption 
and rises with water loss. 
One must doubt the correctness of a fundamental assumption of MULLER 
in determining whether rupture of the coat is due merely to swelling or mainly 
in viscosity and other physical characters, including no doubt breaking strength, 
with temperature, H+, —,and salt content. Again, the actual force with 
which the colloidal contents absorb water varies with conditions. We have 
found” cases where the coats are broken by swelling of the embryo and endo- 
sperm, but it occurs only at 15°C. or above, unless the coat is weakened by 
various treatments, when it occurs at o°C. It is likely that there are cases 
where the seed or fruit contents exert much greater pressure upon the coats 
than those reported by MULLER (3-4 atmospheres). Indeed, CRockER and 
Davis® showed by a very different method that the swelling embryo of Alisma 
Plantago exerts a pressure of about 100 atmospheres against the coat. Soil 
and other natural and applied agents play a much greater part in lowering the 
breaking strength of seed or fruit coats (Alisma, Sagittaria, mantra etc.) 
than MULter found for the seeds upon which he worked. It seems odd that 
MULLER uses the micellar theory in his explanation rather shan applying the 
modern colloid conception. There is no doubt that this leads him to certain 
incorrect inferences, such as cited above. It is very doubtful whether any 
generalizations can be drawn from M@Lier’s measurements, since they cover 
so few forms and in the main the same types of seeds and fruits. For this 
77 Unpublished work by Davis and CROCKER. 
8 Bor. Gaz. §8: 285-321. 1914. 
