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A TEXTBOOK OF THEORETICAL BOTANY 



tinct from all ordinary developments of the testa (Fig. 1365). At one 

 time it was customary to restrict the application of the term to secondary 

 structures arising from the funicle only and to call all others "false arils", 

 but there is no sharp demarcation between them (Fig. 1366). The term 

 caruncle is applicable only to knobby or wart-like arils, associated with 

 the micropyle, while similar warts on the funicle or the hilum have been 

 called by the name strophiole. 



Fig. 1366. — Eiiotiymiis plonipes. Red fleshy capsules opening to disclose 

 the seeds which are co\ered by orange-coloured arils. 



Arils occur on seeds of very many families, of all affinities. They take 

 the form of knobs, horns, bands, ridges or, commonly, cupules, partly 

 enclosing the seed. They are frequently of brilliant colours and contrast 

 with the coloration of the testa, especially in tropical families. They are 

 usually unhardened and frequently contain a store of oil. Occasionally they 

 may serve to attract birds which carry away the seed, or, in smaller seeds, 

 the attraction may be for ants, which are known to carry small arillate seeds 

 like those of Ulex, Cheliduuiiim and Melampyritm for considerable distances, 

 eventually eating the oily caruncles, or elaiosomes as they are sometimes 

 called. This mode of distribution is known as myrmechory (Fig. 1367). 

 A good example of an aril which attracts birds is that of the familiar Euony- 

 miis eiiropaeus, which covers the seed with an orange envelope contrasting 

 strikingly with the red placentae. Arils may serve other purposes directly 

 valuable. Those of Nxmphaea enclose the seed in an air-filled sac which 

 serves as a swim-bladder and keeps the seed afloat for a long time. The arils 

 of Myristica and of some Marantaceae aid by their swelling in forcing open 



