166 DR. FRANCIS DARWIN ON THE MECHANISM ВУ WHICH 
damp sand, and covered with а glass plate; half of the seeds were thrust into the sand* ; 
the rest were allowed to remain on the surface. Contrary to my expectation, the seeds 
exposed to the light began to germinate first. I regret that I did not make a second 
trial with another lot of seeds; I think, however, that the above result is sufficient to 
overturn the theory in question, at least as far as Stipa is concerned t. 
(ii.) The only other hypothesis which I have been able to form is, that by burying 
themselves in the ground the seeds are enabled to escape being eaten by birds. The fact 
that many of them are Graminez, and therefore likely to be sought after as food, favours 
this view 1. | 
The developmental stages through which any structural mechanism has passed is 
alwaysa most interesting question. Unfortunately I am as yet unable to enter into this 
question with respect to the burying seeds. We have seen that the mainspring of the 
mechanism is hygroscopie torsion; now many cells become twisted on drying, such as 
cotton-wool and bast fibres, the tubes of Zrinewn $, and curiously enough the beautifully 
striated cells which support the glands in Byblis gigantea. 
Again, hygroscopic torsion depends оп the spiral striation of the walls of the twisting 
cells. Now lamination or differentiation into more or less watery layers is probably a 
universal condition of the formation of cell-walls ; so that the materials, as it were, for the 
development of hygroscopic torsion are certainly existent. The variability in the torsion 
of the cotton-wool cell shows that a want of unanimity in the direction of torsion would 
be one of the difficulties to be overcome іп the process of development. Through what 
steps the hygroscopic sensitiveness has passed in development I am at a loss to say. 
Finally, I venture to hope that my explanation of the torsion of awns may ultimately 
throw some light оп other forms of torsion; and to this point I hope soon to direct my 
attention. 
% For whatever reason the seed is buried, 16 would seem desirable that it should remain undisturbed. Тһе joint 
by which the awn is attached to the seed seems adapted for this purpose ; for after remaining a few days in damp 
soil the awn сап be detached by the slightest touch. Roux points out the same thing in Erodium. 
+ G. Roux, loc. cit. states that Erodium-seeds germinate better when buried to the “ normal” depth than when 
more or less deeply covered by soil. The details are not given in a manner to carry conviction. 
+ The seed of Anemone montana (one of the burying seeds) contains a large quantity of endosperm ; the seed of 
this species is moreover, as far as I can make out, destitute of the acrid principle so common in the Ranunculacee, 
and which is found at least in some representatives of the neighbouring genus Clematis. Is it possible that the acrid 
principle may serve to prevent animals or birds eating the seeds of the Вапиисшасе» ? as we know to be the case 
with the Bitter Almond (* Variation of Animals and Plants,’ 2nd edit, vol. ii. р. 218). If so, the deficiency in the seed 
of Anemone montana of an acrid principle may be connected with the development of the burying-mechanism. 
$ Sachs, * Physiologie Végétale,’ (translation: Geneva, 1868) р. 453, quoted from Nügeli and Cramer, ‹ Pflanzen- 
phys. Untersuch.’ 
