GRIFFITHS: A NOVEL SEED PLANTER 169 
with the air. The lower layers are the dryest and, therefore, 
soon become attached to particles of earth, we will say 2 mm. be- 
low the surface. As drying proceeds the upper surface in con- 
tact with the air will sink, and the lower anchored to the particles 
below the surface will exercise a downward pull. The lower sur- 
face is drying from below so that successively higher particles are 
being subjected to the downward strain. There are, therefore, 
three forces acting, the first horizontal and outward caused by the 
anchoring of the outer edge of the flattened particle of mucilage, 
and the second downward owing to the contraction of the upper 
layers exposed to the air. The third acts from above downward 
and is the result of loss of water by the lower layers of mucilage. 
It should be stated that the seed is comparatively free from these 
three forces, for it is in the center of the mucilaginous particle which 
is the last to solidify. The resultant of these three forces is evi- 
dently a downward one which effects the solidifying of the soil 
below and immediately surrounding the seed to a depth of about 
0.5 mm., or equal to the distance between its flat surfaces. All that 
is now necessary in order to have the planting completed, is to 
have a gust of wind or a shower of rain pack the soil around the 
seed in its little depression. 
To summarize, therefore, it appears that the function of the 
mucilage is the burial of the seed and that this is accomplished by 
the tension set up owing to the contraction of the expanded muci- 
lage which has become firmly attached around its outer and lower 
edges to the particles of soil into which it has penetrated, resulting 
ina Compacting of the soil immediately below the seed and its 
Coat so as to form a pit into which the seed is forced. The cup- 
shaped depression is subsequently filled with earth by entirely ex- 
ternal influences, 
On the Arizona deserts this phenomenon is not confined to the 
Ordinary soils of the mesa, but may frequently be observed on the 
hard surface of a roadbed. To what extent this principle is appli- 
cable to flax, pepperwort and other mucilaginous seeds has not, 
So far as the writer knows, been investigated. 
