328 CONTRIBUTIONS FROM THE NATIONAL HEEBAEIUM. 



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, bony shell almost half an inch in thick- 

 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 cotyledon, which 

 grows down into the ground for a distance of from 3 to 6 inches 

 (pi. 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 (pi. 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 of permanent moisture in the soil and establish itself on 

 a self-supporting basis. 



