CERTAIN SEEDS BURY THEMSELVES IN THE GROUND. 151 
out * that the long feathery awn of Stipa serves as a “ Verbreitungsmittel," or means of 
distribution. It is found that seeds dropped from a height of a few feet usually preserve 
a nearly vertical position, and strike the ground with their point. Moreover, if they are 
allowed to fall among low vegetation they are caught by the knees (2, 4) or by the 
feather, and are fixed in a more or less oblique position, the seed resting on the ground. 
Many seeds would no doubt escape being entangled; and many others would be caught 
in unsuitable positions—suspended in the air, for instance, or making too acute an angle 
with the ground, or resting on some hard impenetrable body. Neverthelsss many seeds 
are undoubtedly caught and held fast in suitable positions. The great length of the 
feather (nearly 30 cm.) would render entanglement in low vegetation an easy matter; 
and when a seed is once entangled the hairs serve to hold it fast and prevent the wind 
blowing it away. 
In order to ascertain what would occur under these circumstances, I made experiments 
of the following kind :—A vessel being filled with dry sand or light soil, two upright 
sticks were fixed at about a centimetre apart; and these were connected at the height 
of 8 or 9 сш. from the surface of the soil by a cross pin, a second one being fixed 
2 ог 3 cm. higher up. The Stipa-seed is then placed with its point resting on the soil, 
and its feathery awn passed through the loophole between the two supports and the two 
cross pins. The whole is now placed under a bell glass lined with wet blotting-paper. 
This is better than wetting the awn directly; for in touching it with a wet brush it is 
possible to push it into the soil without being aware of it, and in syringing it the soil 
may become too much wetted. In order to dry the awn it is merely necessary to 
remove the glass; thus by alternations of dryness and moisture the awn is made to twist 
and untwist, just as it would under the changing hygrometric conditions of dew and 
sunshine in a state of nature. The amount buried may then be measured with a pair 
of compasses. It is very important to estimate the amounts buried, by measuring from 
the surface of the soil to the top of the seed, and not to any marked point in the амп; 
for in the latter case the measurements will be obviously inaccurate, owing to the 
lengthening and shortening of the awn. 
All the movements of the awn are far more conveniently studied when the seed is 
fixed and the feather free to rotate; and in taking the times of rotations &е. I have 
found it best always to employ immersion in water in preference to exposing the awn to 
a damp atmosphere; for by the former means a constant amount of moisture is secured, 
and in nature the awn must be frequently exposed to an amount of moisture practically 
equivalent to immersion. 
A dry Stipa-awn plunged into water at the temperature of the room began to 
rotate within a second of its immersion, and untwisted at the rate given in the fol- 
lowing table :— 
* Verbreitungsmittel der Gramineen-Früchte, Bot. Zeit. 1872, No. 49. 
SECOND SERIES.—BOTANY, VOL. І. 
