268 BOTANICAL GAZETTE [OCTOBER 
He suggests that enzymes are produced readily in the lower seeds 
and that, therefore, they have foods at hand to begin their growth 
immediately; whereas the upper seeds are able to develop digestive 
ferments only after a long period of rest, and hence their germina- 
tion is delayed one or more years. This theory has its experimental 
basis in the fact that if both sorts of seeds are exposed to germinative 
conditions for some time the lower ones show much reducing sugar, 
while the upper ones have only a trace. My interest in this problem 
was aroused by ArrHur’s paper on the cocklebur, and the work 
was begun for the purpose of testing this enzyme theory and deter- 
mining definitely the cause of the delayed germination of the upper 
seed, 
II. Materials and methods. 
Most of the germinative tests reported in this paper were made 
between moist filter papers, but in all these cases corresponding tests 
with very similar results were made in fine quartz sand and in garden 
soil. For Avena fatua, Iris, and cocklebur seeds in the bur, all tests 
were made in sand and garden soil on account of the great liability 
of these structures to be attacked by fungi. 
Five species of cocklebur were used: Xanthium canadense Mill., 
X. echinatum Murr., X. glabratum (DC.) Britton, X. glandulijerum 
Greene, and X. speciosum Kearney. In each species similar 
conditions gave similar results whether the seeds were in the bur or 
removed from it; but for convenience in handling and accuracy of the 
records the seeds were generally removed from the bur. For testing 
increased oxygen pressures the soaked seeds were allowed to rest 0m 
the walls of flasks containing oxygen or (in the checks) air. Germ 
native tests at high temperatures were made in ordinary paraffin ovens 
regulated to the desired temperature. The effect of temperature 07 
the rate of diffusion of oxygen through the seed coats of the cocklebur 
was determined in a large water bath (such as is used in chemical 
laboratories for determining solubility, etc.) regulated to 0.01". 
The seeds used were collected when thoroughly ripe from various 
parts of the United States and Europe,’ stored in a dry room, 4? 
used in experimentation within six months after collected. since 
a year of dry storage and the region from which the seeds were 
«Iam indebted to M. P. Dreuponné for collections from Belgium. 
