THE ANGIOSPERMAE 



H93 



the dehiscent pericarps and may thereafter, when exposed, also attract birds 

 by their bright colours. Whether the chalazal wings of the seeds of Brome- 

 Haceae, which are wind-dispersed, should be called arils is doubtful. They 

 originate before fertilization, but so do many of the arillar coverings which 



i t f • • # 



Fig. 1367. — Seeds with oily caruncles which may act as attractions in aid of dispersal. 

 Top : RicinKs communis. Bottom : Ulex eiiropaeus. 



grow from the exostome lips at the micropyle (Euphorbiaceae). In some 

 V2LTp\\\on-iiCQ^t{e.g., Sarothamnus scopariiis) there is an arillar swelling in the 

 form of a cup, where the funicle joins the seed. This is supposed to assist 

 in detaching the seed by constricting the funicle. The corky aril in Caltha 

 keeps the seeds afloat in water and thus aids in dispersal. 



A unique function is fulfilled by the aril in Opiintia. The seed is 

 circinotropous, the funicle surrounding the ovule. From the funicle 

 grow out two wing-like expansions which finally envelop the ovule com- 

 pletely, leaving only a narrow slit through which the pollen tube enters 

 and, subsequently, the primary root emerges. This envelope hardens and 

 forms the efl^ective testa of the ripe seed, the integument being only a thin 

 membrane. 



Particularly well known is the aril of Myristka fragrans, the Nutmeg, 

 cultivated as a spice in S.E. Asia. The ripe seed is about an inch long and 

 is surrounded by an aril which grows from the funicle and extends towards 

 the micropyle as a circle of fleshy fingers which anastomose in an irregular 

 network (see Fig. 1471). When dry it turns golden orange and is rich in oil. 

 The aril yields the spice called mace and it is used as well as the nutmeg 

 seed. In the species of Passiflora which have edible fruits [P. ediilis and P, 



