Palms of Puerto Rico 543 



3. Practically the difference in width is still greater because the 

 segments of Thrincoma are never fully expanded but remain deeply 

 channelled, thus decreasing the area of exposure to the wind and 

 increasing the rigidity of the leaf. 



4. Resistance to the wind is also reduced in the tall species by 

 the separation of all the segments to more than two-thirds their 

 length, while in Thrinax praeceps the median segments are united 

 more than half way up. In the latter, as in the other members of 

 the group, the separation begins at the point of greatest width of 

 the segment, but as if to show that the deeply divided leaves of 

 Thrincoma are an adaptation, the greatest width is located near the 

 longitudinal middle of the segments, 10 cm. or more above the 

 bottom of the cleft. 



5. The texture of the leaf of Thrincoma is thicker and firmer 

 so that the segments generally remain straight to the tips while 

 in Thrinax they often droop after the leaves have become fully ex- 

 panded. 



6. The color of the leaves of the tall palm is a very dark green 

 while those of Thrinax praeceps are uniformly of a much lighter, 

 fresher tint. 



7. The veinules of the firm leaves of Thrincoma are more 

 numerous and closer together than those of Thrinax. 



8. The veinules are also subequal in size, giving an appear- 

 ance of uniform pattern, while in Thrinax praeceps from 3 to 5 of 

 the veinules of each side of the midrib are distinctly larger than 

 the 'others, the larger veinlets being separated by from 3 to 1 o 

 smaller ones. 



9. In Thrincoma the cross-veinules are scarcely visible to the 

 naked eye ; under a lens they are still obscure, never equalling in 

 size the smaller of the longitudinal veinules, which they seldom 

 appear to cross. In Thrinax praeceps, on the contrary, the cross- 

 veinules are as large as the finer longitudinal ones ; they are obvious 

 without a lens and give the fabric of the leaf a peculiar marbled 

 effect on account of the fact that they are generally oblique or 

 wavy and commonly appear to cross several of the longitudinal 

 veinules. 



10. The margins of the segments are thickened in both 

 species, and on the upper side there is a groove inside the mar- 



