Jan. io, 1914 
Drought-Resisting Adaptation in Maize 
295 
tion satisfactory to all morphologists seems very remote. With organs 
that pertain to the very beginnings of the plant, even the primary dif¬ 
ferentiation into root, stem, and leaves may not be complete, and to 
insist on a definite classification of these primitive organs may be idle. 
Studies of seedlings of Hopi maize show that the mesocotyl may fre¬ 
quently develop up to lengths of 36 cm. / and it has been possible to note 
a fact which appears thus far to have escaped notice—namely, that the 
mesocotyl may give rise to roots at any point on its surface—but these 
roots are threadlike and do not resemble the roots that arise from the 
nodes of the culm. They do, however, closely resemble the roots that 
arise from the radicle immediately below the seed. (See PI. XXIX, 
fig. 1.) In grasses roots usually arise from nodes, not from internodes, 
and the presence of roots on this organ in maize distinguishes it sharply 
from subsequent internodes and is an argument in support of the inter¬ 
pretation that this intercalary growth, long though it is, is really a part 
of the cotyledon and may properly be termed a mesocotyl. A further 
reason for retaining the term “mesocotyl” is because the interpretation 
implied by its use permits more direct comparisons with other groups 
of monocotyledonous plants, where the organ sheathing the plumule 
seems undoubtedly to be a part of the cotyledon. 
From observations upon many varieties of maize it has become appar¬ 
ent that when a grain of corn germinates in the ground this usually insig¬ 
nificant organ is of vital importance to the life of the plant, for it is 
through the elongation of the mesocotyl that the shoot is enabled to 
reach the surface. So long as the seedling remains below ground, away 
from light, the mesocotyl will continue to elongate until it reaches a 
maximum length, which we have found to differ in different varieties, 
but which seems reasonably constant within the variety. As the meso¬ 
cotyl elongates, the coleoptyle, with its firm, sharp point, is pushed 
upward through the soil. As soon as the coleoptyle emerges from the 
soil, the elongation of the mescotyl ceases, and elongation of the inter¬ 
node bearing the first true leaf begins, forcing open the coleoptyle. 
If the seed is planted so deep that the maximum elongation of the 
mesocotyl, which in anatomical structure shows a striking relation to the 
radicle, fails to bring the coleoptyle to the surface, the task of penetrating 
the soil and reaching light devolves upon the first true leaves. In com¬ 
parison with the sharp coleoptyle, these leaves are but poorly adapted 
for forcing their way through the soil, and if the tip of the coleoptyle 
stops more than a few centimeters below the surface these leaves usually 
crumple and never reach the light. 
In the varieties of maize commonly grown we have been unable to force 
the mesocotyl to a length greater than 10 cm., while in the Hopi and 
Navajo varieties this usually minute organ has in our experiments fre¬ 
quently reached the enormous length of 25 or even 30 cm. 
1 In Euchlaena also the mesocotyl may reach a length of 28 cm. Van Tieghem gives 3 cm. as the maxi¬ 
mum length of this organ in grasses. 
