ACANTHACE^E 349 



ally with some force, the valves carrying with them the seed- 

 bearing half-placentas. The seeds vary in number as the 

 ovules, but are frequently fewer by abortion. In Thunbergia 

 and in the tribe Nelsoniese they are globose or orbicular and 

 dor sally compressed with a ventral hilum. In other tribes 

 they are laterally compressed and ascending, with the hilum 

 basal and marginal. The funicle is hardened and incurved, 

 forming the hook-like process (retinaculum) upon which the 

 seed is borne ; sometimes this hook is produced beyond the 

 point of attachment to the seed. The testa is membranous or 

 thickened, often variously corrugated or raised into little points; 

 it is sometimes smooth or covered with mucilage which when 

 dry forms a covering resembling adpressed hairs. Endosperm 

 is wanting except in the species belonging to the tribe Nel- 

 soniea3. In other groups the embryo occupies the whole of 

 the interior of the seed, and conforms to its cavity. The 

 cotyledons are orbicular, flat or plano-convex, and cordate at 

 the base. The radicle is short and straight or bent obliquely 

 to the axis of the cotyledons, and occupies the basal notch of 

 the latter. 



The ovule, embryo and seed are often variously abnormal 

 in the tribes Thunbergieas, Nelsoniea? and the subtribe Andro- 

 graphidefe. The ovules for instance of Thunbergia fragrans 

 are amphitropous ; the seeds are orbicular, dorsally compressed 

 and concave on the ventral face where the hilum is situated. The 

 embryo occupies the whole interior of the seed and is concave 

 on the ventral aspect in conformity with the seed. The 

 cotyledon on the ventral aspect has its edges recurved, 

 partly covering the outer one on the dorsal aspect. 



About four other types have come under my observation. 

 The ovules of Acanthus spinosus are amphitropous or semi- 

 anatropous and twin in each cell. The embryo is trans- 

 versely oval and slightly emarginate in a young state, gradually 

 becoming more orbicular as it reaches maturity, and the 

 radicle is wholly included between the close-fitting auricles 

 of the cotyledons. This is better seen in the longitudinal 

 section of the seed of A. longifolius (fig. 579) which has trans- 

 versely oval cotyledons somewhat indented near the chalaza, 

 and deeply auricled around the radicle. They are piano- 



