32 



to the exclusion of everything else, and in such situations it is 

 the finally established native vegetation following the ohia lehua 

 forest and is considered to be the ultimate forest type. 



FOLIAGE. 



The koa appears still to be in a process of evolution, for it 

 has two kinds of leaves. The true leaf of the koa, which ap- 

 pears first upon the germination of the seed, is a compound bi- 

 pinnate leaf. These are soon replaced as the tree grows, and the 

 foliage matures into phyllodes which are the leaf stalks dilated 

 into flattened stems and which in themselves become leaves and 

 perform the usual functions of leaves. Although these are not 

 true leaves, they are referred to as such in the first part of this 

 article. 



The true, compound leaf is found on young seedlings and on 

 larger trees near the ground, where there is shade and moisture. 

 They also are found springing from adventitious buds near the 

 base of the trunk. As the foliage becomes more exposed to the 

 light and heat these true, tender, compound leaves take on the 

 new form of sickle-shaped phyllodes, which are coarser and more 

 heat-resisting. Xerophytic conditions are responsible for the 

 cause of the change from true leaves to phyllodes, a character- 

 istic which was probably not evolved in Hawaii, but inherited 

 from its ancestor on Australian soil. The Hawaii variety of 

 koa develops very broad phyllodes at the higher altitudes, where 

 there is more moisture in the form of fog and mist. 



SEEDS. 



The blossom of the koa consists of a small, densely globose, 

 flowered head of a yellowish color, which develops into flat 

 pods or legumes up to six inches long, brown in color, and 

 which usually open on the tree. In each pod there are up to 

 12 seeds, which are flat, hard and shiny, and dark brown to 

 black in color. The seed of the koa on Oahu is brown, about 

 the size of and resembles an apple seed. The Hawaii variety 

 of koa has a seed twice the size and is darker, while the seed 

 of Acacia Kauaiensis is almost round, flat, and black. The 

 horny seed often remains on the tree for a year after it ripens, 

 and when lying dormant in the ground it is known to have re- 

 tained, for a period of 25 years, its ability to germinate. To 

 hasten sprouting when planting the seed, it is necessary first to 

 soak it for 24 hours in very hot water. 



INSECT ENEMIES. 



As the seed pods mature they are attacked by the larvae of 

 four different species of Tortricid moths, which feed on the 

 young growing seeds, working from one to another until often 



