DB. R. SPRUCE ON EQUATORIAL-AMERICAN PALMS. 95 



m 



abortive, or even obsolete, in the lower part of the branches of the 

 spadix, leaving tJie 5 Jlowers solitary/ in or on their receptacle ; 

 while in the upper part of the same branches it is the § flowers 

 that disappear, and the c? floivers tliat remain standing thereon in 

 pairs. This is the usual structure in the Cocoina3, e. gr. in Baciris^ 

 Attdlea^ &c. ; and in the imbricate-petaled Arecinse, such as Euterpe^ 

 (Enocarpus^ &c. ^ 



In other palms all the triplets of flowers, by the abortion of one 

 sex or the other, will become unisexual on the entire spadix, 

 causing some spadices to be solely male, with twin flowers, others 

 female, with solitary flowers. This occurs most frequently in 

 Geonoma and its allied genera Leopoldiniay Nwnnezharia^ &c., where 

 the female flowers may be actually present on the male spadix, but 

 remain effete between the pair of perfect females; and on the female 

 spadix the male flowers, one on each side of the perfect female flower, 

 never emerge from the alveole, but wither away unopened ; or the 

 flowers of the missing sex may be really obsolete. This gives 

 rise to a very curious phenomenon which I would call 



" Alternation of function P 



I first ascertained its existence when at San Carlos del Eio 

 Negro, near the debouchure of the Casiquiari, in this way. In 

 May, 1852, I found a small plot of ground in the forest covered 

 Avith plants of a delicate palm, a species of Geonoma^ growing 

 about ten feet high. The plants were all females, and bore young 

 fruits. On revisiting the spot in the same month of the fol- 

 lowing year, \ saw, to my astonishment, the very same plants 

 all bearing male flowers alone ! But the mystery disappeared when, 

 on examination, I made out that male and female spadices must 

 have alternated all the w^ay up the stem. Afterwards I found that 

 the same, or a similar alternation of function existed in many 

 other palms, and that plants exercising {pro tern.) the male func- 

 tion stood rarely far apart from others exercising the female 

 function. The follomng are the types of alternation that have 

 fallen under my notice : — 



$ '-^ (5 in Geonoma discolor and other species. 



$ -- $ d* in 6^. paniculigera^ chelidonura, &c. 



cJ -- $ c? in Maximiliana regia and some other palms. 



It is quite possible that extended observation might disclose 

 the existence of all these modes of alternation iu one and the 

 same species ; and I suppose they must all be regarded as inter- 



