CERTAIN SEEDS BURY THEMSELVES IN THE GROUND. 155 
The free end Е is now supposed to rock backwards and forwards, describing ares alter- 
nately in directions $ & i 7, in the plane of the paper and about the point P. When 
Е moves in direction ¿ the barbs ddd will offer little resistance, whereas the barbs 
cee will in fact act like fulera, and will enable P to be forced deeper into the ground. 
On the movement being reversed, this action will be reversed also, 444 giving the 
fulera, and P being again buried deeper. Although the tendency of а Stipa-awn, on 
drying, is to move (not backwards and forwards in one plane, but) so as to describe a 
cone, yet I believe the above-described process is essentially what occurs in Stipa; for 
the seed is revolving in soil of densities varying at different points, so that it moves not 
regularly, but by jerks; moreover the plume is rather more developed on two of the 
opposite surfaces of the seed than on the intermediate regions, and the point is obliquely 
set оп. In observing the process of drying, I have often seen a distinct rocking move- 
ment as the awn attempted to rotate and was continually forced back again. All their 
aberrations from a structure and from a rotation of mathematical regularity must favour 
the levering or wriggling movement of which the diagram in the woodcut gives the 
essential action. 
In describing the manner in which the seed of Hrodiwm is buried during drying, Han- 
stein does not enter into any of the above considerations as to a rocking movement &c. ; 
he merely says that * the lower part of the awn begins to contract into narrow spiral coils, 
causing the cone (i. e. seed) to turn on its axis and penetrate the ground; and the егесі 
hairs on it, which point upwards, retain it there like grappling-hooks ”%, 
It has now been shown by what means the seed of Stipa is buried, both as it untwists 
and also as it returns to a state of torsion. Ву a combination of these two processes, the 
awn is thrust into the soil to such a depth as to cover up the seed completely. Thus, in 
an experiment, in three wettings and three dryings 28 mm. was buried in dry sand: the 
ordinary length of a seed is 17 mm.; so that this is amply sufficient. In another experi- 
ment a seed of 16 mm. length was completely buried in three wettings and three dryings. 
Another seed, which I entangled in the branches of a low bush, and left out of doors for 
eight days, had buried itself to a depth of 31 mm., impaling a piece of rotten leaf on its 
way. Mr. Farrer informs me that the Stipa-seeds which blow away from the parent 
plants succeed in burying themselves in his garden. The question of what advantage 
it is to the plant to bury its seeds will be discussed in the sequel. 
Before passing on to describe the arrangement of structure of which the hygroscopic 
mechanism consists, I shall give a brief account of the phenomena exhibited by the 
Stipa-awn, considered merely as mechanical actions, and with no reference to the biolo- 
gical conditions in which they occur in Nature. 
A simple instrument was made for me by my brother Horace: a piece of Stipa-awn, 
about 5 em. in length, was employed, taking care to avoid either of the knees (k, ог kə). 
The awn is fixed at one end, and at the other bears a light index, fitted to travel round a 
clock-face as the awn twists or untwists; the bearing of the awn is so managed that the 
whole of it can be immersed in different fluids. The S¢ipa-awn is hygroscopically ex- 
* Sachs, p. 841, Eng. Transl. (a perfectly correct abstract of the original). 
