328 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
seedling against drying out would be of the greatest possible advan- 
tage. An evolutionary tendency in this direction would be favored 
by natural selection and might be expected to make rapid progress. 
The natural result would be that we should have one species highly 
adapted in one respect, but remaining otherwise closely like its rela- 
tives, as in the case of the coconut. The adaptive value of the husk 
as an expedient for germination can also be estimated by comparing 
the habits of the coconut with those of related palms that encounter 
similar environmental problems. 
Excellent examples of adaptive germination devices are afforded 
by Attalea and Acrocomia, two relatives of the coconut found in 
Guatemala. The seeds of Attalea cohune, which abounds in eastern 
Guatemala, are about the size of a turkey’s egg, with a thin woody 
husk and an extremely hard, beny shell almost half an inch in thiek- 
ness, perforated at the base for the exit of the embryo. But instead 
of pushing out a young plant as in the coconut, the first organ to 
emerge from the seed is the long, slender, cord-like cotvledon, which 
grows down into the ground for a distance of from 3 to 6 inches 
(pl. 60). The true germination takes place at the end of this burrow- 
ing organ, so that the young plant, though produced from a seed 
lying on the surface of the soil, is well and deeply planted, and at 
once sends its roots still farther down to establish communication 
with the permanent moisture of the deeper layers of the soil. The 
cord-like cotyledon connecting the seed with the young plant remains 
alive for a long time, to carry down food materials from the store- 
house above. 
In Acrocomia the same difficulties have been solved in a very 
different way, though not less definitely adaptive. The nursing foot 
or cotyledon is very short and remains functional for a much briefer 
period than in Attalea. The young plant completes its germination 
and begins its development close to the surface of the soil. It par- 
tially supplies the deficiency of the length of the cotyledon by growing 
downward at first instead of upward, the bases of the leaves being 
abruptly bent (pl. 61). These first joints of the seedling very soon 
thicken into a fleshy bulb, formed, doubtless, by a prompt transfer of 
the nutrient material stored in the seed, thus avoiding the need of a 
long-lived cotyledon as in Attalea. 
The coconut follows neither of these policies. Being provided with 
its own water supply inside and outside the nut, it is able to grow a 
plant of considerable size before attempting to make any connection 
with the soil. And then being thoroughly prepared, and the proper 
season having arrived, it is able to send down a good supply of roots 
to the level cf permanent moisture in the soil and establish itself on 
a self-supporting basis. 
