ECOLOGY 137 
varieties of maize are unable to force the mesocotyl to a 
length greater than 10 em. (Collins, Journ. Agr. Res. 
1: 293. 1914). 
172. Impervious seed-conveyers—At maturity all 
seeds are moderately dry within, that is, for the preserva- 
tion of the endosperm during the dormant stage the moist- 
ure has been reduced to a minimum. To protect the 
contents against further loss of moisture which would 
injure or kill the embryo, the seed is enveloped by an 
impervious coating, which serves the double purpose of 
preventing the loss of moisture from within and the 
absorption of moisture from without. The protecting 
coating may be in immediate contact with the seed or it 
may be developed from some outer coating or organ. If 
an outer coating such as the glumes become hardened for 
this purpose, then the inner organs, lemma and pericarp 
are comparatively thin. 
The protective coating is developed from the seed-coat (Sporo- 
bolus), pericarp (wheat), lemma and palea (Panicum), glumes 
(Andropogon), rachis and glume (Tripsacum), sheathing bract 
(Coix), involucre (Cenchrus), or various combinations of these. 
In some cases, as in Cenchrus, several seeds are protected by the 
same outer coating. 
173. Self-burial.— The dormant stage continues 
through the season unfavorable for germination, that. is, 
winter or a dry season. When the season for germination 
arrives, the seed, under the influence of moisture and 
higher temperature, gradually absorbs water, growth is 
started, the embryo swells and bursts through its sur- 
roundings, and germination has begun. Ordinarily the 
seeds are more or less covered with earth or debris by the 
action of the wind. But some seeds are aided in self- 
burial by the torsion of the awns they possess. The awns 
