‘I916] CURRENT LITERATURE 161 
cause he claims is age, not the absolute age of a species, but its age in the 
locality. Thus eoceant species are rare because they are “in the earlier 
stages of spreading.’ 
WILLIs treats the two main objections to his theory as follows. The claim 
that the endemic species are really the oldest he answers with the evidence that 
t 
merely the claim for natural gine is that local species develop in response 
to local needs or conditions; but Lis finds that endemic species of a given 
a spread over an area of given ak although it may contain other 
of soils, climates, and floras. Also the geographical boundaries of various 
abi species do not coincide; that is, the species do not occupy jointly 
areas where special local conditions may exist. The arithmetical regularity 
of distribution of species within the various ‘rarity classes,” and the geometrical 
regularity of the species boundaries, irrespective of physiographic or meteoro- 
logic conditions, must be explained by the mechanical, undifferentiating result 
of age. 
In accordance with this theory, the figures given by WILLIs show that 
parasites, saprophytes, and climbers are “rarer” than independent plants, as 
should be expected, for they must have followed the others historically. It 
Iso appears that among water plants the dicotyledons are more common 
ngiosperms in 
WILLIs found no species that was “dying out.” He believes that species die 
out only by accident, a more extensive accident sins odparasenté for the dis- 
appearance of a ‘‘common” species than for a “rare one.”—MERLE C. 
COULTER. 
Securing complete el difficulty often encountered by the 
geneticist is the failure of many seeds to germinate with desirable promptness. 
It is well known that in certain species of Oenothera, half or more of the seed- 
like structures contain no embryos, and that in many cases those seeds which 
do contain embryos are subject to delay in germination. Dx Vries* has found 
that in many cases he can more than double the number of prompt germina- 
tions by soaking the seeds for 2 days in water and then subjecting them sub- 
merged in water for 24 hours in an autoclave to a pressure of 6-8 atmospheres. 
The author assumes that the effect is due to the forcing of the water need 
for germination through minute rifts in the hard portion of the seed coats. 
He gives a number of instatices to show the contrast between seeds merely 
soaked, and those which have been subjected to pressure. In certain cases 
he found it advantageous to subject the seeds a second time to pressure. A 
very small percentage of the seeds resisted this treatment. 
* De Vartss, H., Uber kiinstliche Beschleunigung der Wasseraufnahme in Samen 
durch Druck. Biol. Centralbl. 35:161-176. 1915. 
