33 
Longevity and Vitality of Seeds. 
The tissues of the embryo of Leguminosae were found by con¬ 
trast to have a system of fine intercellular spaces and be quite 
porous so that air is readily sucked through a piece of the cotyledon 
of a pea or bean. 
A really dry seed is thus isolated from gaseous exchange with 
its environment. “ Air-dry ” seeds in the condition in which they 
are usually stored contain, however, from five to fifteen per cent, of 
imbibed water, and their integuments may not be quite impervious 
to air. Seeds are indeed very hygroscopic and absorb water in pro¬ 
portion to the humidity of the air. Jodin 1 has recorded the varying 
weight of seeds in different meteorological conditions, and one 
of the few changing factors in an ordinary resting seed stored in 
air must be this alternate taking up and giving off of water. It has 
been suggested that the ceaseless slight molecular changes involved 
in this process slowly disorganise the viable protoplasm and in time 
cause the death of the seed. From such changes a “ hard ” seed 
would be exempt. It is therefore probable that complete dessication 
and preservation in a dry environment are necessary conditions for 
testing the maximum longevity for any plant whose seeds are among 
the majority in which the testa is not impermeable to water. 
Extensive tests have not yet been made on these lines, but 
some have been started by Becquerel. 
Complete dessication is a lengthy process which can be accom¬ 
plished by maintaining the seeds for three months in a vacuum at 
45"C in presence of caustic baryta. Hard seeds must have their 
testa perforated before they can be dried at all. 
It has been maintained that seeds preserve their vitality longer 
if buried in natural damp soil, but it seems clear now that this is 
the exception and that most keep better dried (Duvel, U.S. Dept, of 
Agricult., Bull. 83, 1905). 
There are a great many cases recorded in journals in which it 
is concluded that seeds must have been preserved alive for very 
long periods, perhaps many centuries, buried more or less deeply in 
the earth. Cases in point are the appearance of plants unknown in 
the district on the mud dredged from Poole Harbour and spread on 
the surrounding land (Salter, Journ. Linn. Soc., 1845) ; and a 
similar phenomenon on the Avon at Bristol (White, Trans. Brist. 
Naturalists’ Soc.). 
In a case recorded by von Heldreich the definite longevity of 
1,500 years was claimed for the seeds of Glaucium Serpieri. This 
plant, then unknown in Greece, appeared in quantity when the 
heaps of refuse from the classical silver mines at Laurium were 
cleared away from the surface of the ground in the nineteenth 
century. 
In such cases it is impossible that there should have been 
adequate supervision, and it will not do to attach credence to the 
extreme examples ; further it is found now by experiment that the 
plants recorded as appearing in most such cases have not hard 
seeds and shew no particular longevity—at least when preserved in 
air. 
Another well known class of cases is the appearance of 
unaccustomed plants on the soil cleared by forest fires. Ewart has 
found hard seeds of Acacia spp. buried deeply in forests where there 
were no such trees within a mile, and he has also determined the 
1 Ann. agronomiques, T. XXIII, 
