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206 MERRILL. 
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the strand flora and mangrove vegetation, mentioned above. 
Of the remaining 30 per cent of the introduced element, very 
many of the species, although not flowering all the year, have 
decidedly prolonged periods of anthesis, such as Enterolohium 
saman Prain, 7 months, from March to September, Delonix regia 
Raf., 5 months, from March to July, etc. 
■ There are various reasons that will in part account for this 
enormous difference in continuous anthesis between the indi- 
genous and the introduced elements. For instance, many of the 
cultivated plants are comprised in the latter group, and these 
are always under more or less abnormal conditions, while very 
many of them have been greatly altered by the process of selec- 
tion in the course of domestication. In those species that are 
cultivated for their ornamental flowers, unquestionably the very 
fact of continuous anthesis has in many cases been one of the 
reasons for their original selection and domestication, their 
popularity as ornamentals, and hence their wide distribution. 
A considerable number of these plants locally never produce 
fruits, such as several species of Hibiscus, Ixora' finlaysoniana 
Wall., /. chinensis Lam., J. coccinea L., Odontonema nitidum 
0. Ktz., Gr^ptophyllam pictum GrifF., Thunhergia grandifiora 
Roxb., r. erecta And., Ipomoea cairica Sweet, Barleria cristata 
L., Allamanda cathartica L., A, hendersonii Bull., and many 
others, and this very fact unquestionably has its influence on 
the question of continuous anthesis. The above factors, how- 
ever, can explain this striking difference in anthesis only in 
part. 
It is impracticable, if not quite impossible, to determine the 
nature of these plants in their native homes as to restricted or 
continuous anthesis. Doubtless some of them in their original 
habitats flower all the year, but it is most probable that the 
great majority of them were originally species with restricted 
anthesis, a character which has undergone extension or modi- 
fication due to changed environment and climatic conditions in 
their new homes. 
Whatever may have been the causes leading to the develop- 
ment of this character the fact remains that most of our ubiqui- 
tous tropical weeds owe their success largely to the fact that 
for twelve months in the year they are Continuously developing 
and maturing seeds, giving such species an enormous advantage 
in the struggle for existence over those having a restricted 
period of anthesis. Naturally also this continuous seed produc- 
tion gives such plants a great advantage over native species, 
