1g2 BOTANICAL GAZETTE [MARCH 
matter of fact, I have not found as yet any essential differences 
between the two groups; but the doubt remained that such might 
still be discovered if it were possible to bring to germination all, or 
almost all, the slow seeds of a given sample. For a number of 
years I have tried various means to reach this end, but only of 
late have I succeeded. 
It is a well known fact that many kinds of hard seeds may be 
induced to germinate by means of filing. Filing machines, espe- 
cially for the smaller leguminous seeds, are now often used in 
agricultural practice, the best known one being the Swedish type, 
constructed by HJALMAR Nitsson, the Director of the Swedish 
Agricultural Experiment Station at Svaléf. It files the seeds in 
a continuous current by throwing them against a rapidly revolving 
filing disk. Unfortunately, in the seeds of the evening primroses, 
the hard layer is not the external tissue, but that of the inner 
integument. The outer coat thus prevents the filing, and experi- 
ments which Professor Nitsson has had the kindness to make for 
me with his apparatus did not give the desired result. 
In the soil the water is imbibed into the seeds through micro- 
scopic and very narrow slits in the hard layer. It is assumed that 
these slits are filled with air which, in the narrower ones, is a power- 
ful obstacle against the penetration of the water. So long as this 
only reaches the cuticularized parts of the walls of the slits, no 
moisture can reach the embryo and this remains dormant. The 
question, therefore, is to compel the water to penetrate into the 
deeper parts of the slits so as to reach the spots which can be 
moistened. 
In order to solve this difficulty, I have tried pushing the water 
into the slits under a high pressure. A compression of the sur- 
rounding air to 6-8 atmospheres has proved to be sufficient to 
induce all or almost all the healthy seeds to germinate in a few 
days. The apparatus used is a combination of an autoclave with 
an air-pump such as is used for automobiles, and the model known 
as the Michelin pump seems to be the easiest and cheapest avail- 
able one, while any autoclave, as, for example, an ordinary steam 
sterilizer, will answer the purpose. Mine has 20 cm. inside diam- 
eter, and can be filled to 8 atmospheres in about five minutes. 
