1906] CROCKER—DELAYED GERMINATION 273 
The measurements of the three layers are approximately as follows: 
the outer layer, at the radicle end 100 », at the distal end 20 #; the 
middle layer, at the radicle end 15 p», at the distal end 8 »; the inner 
layer, at the radicle end 30, at the distal end 4. The middle 
layer is somewhat thicker in the upper than in the lower seed. In 
both seeds it is less dense at the distal end. It seems probable that 
the denser middle layer is only partly permeable to oxygen, less so 
in the upper than in the lower seed, and less so at the distal than at 
the radicle end. This accounts for the increased oxygen pressure 
initiating the growth at the distal end. 
Gaseous exchanges in res piration—The two sets of experiments on 
the gaseous exchanges of the seeds in respiration throw some light 
on the effect of the seed coats, The first set, reported in Table V, 
a. of the oxygen taken up with the seed coats removed 
esha up with the seed coats intact. Only the ratios can be 
1 eagle ere, for different weights of seeds were used in the four 
eterminations. These measurements were made with 
eudiometers, 
r TABLE V. 
ABs ue 
ORPTION OF OXYGEN; SEED COATS INTACT AND REMOVED; TEMP. 23°. [> 
Cc. OF OXYGEN 
Ratio oF I to IT 
SEEps UsEp ee TAKEN UP AFTER 
‘., 6 hrs. | 22 hrs.| 6 hrs. | 22 hrs. 
wi —_——— 
er seeds, Au. Canadensis removed I gis: 142.6 
Low : intact II 1.6 6. 1.6 1.8 
€r seeds, X. echinatum............. removed I | 12.2 : 
Upper intact II AE p 
re eS glanduliferum.......... removed I ae it.6 é 
U : intact II 2.1 ha ea a. 
Pper seeds, X. SCnMathiy oe ts ape removed I | 9.4 4 
intact II 4.8 Gag]. 2b 28 
Pic - % indicates, the lower seeds at 23° take up 1.6 to 1.7 
Coats intact . ne gen with the seed coats removed as with the seed 
oxygen ‘tia, <. ile the upper seeds take up 2 to 2.4 times as much 
ratios are pp Ne seed coats removed as with them intact. The 
between ti Pe ly much smaller than would obtain in the soil or 
of the eud; ter papers, for the coats of the seeds lying on the walls 
lometer, though in a theoretically saturated atmosphere, 
