368 SYSTEMATIC BOTANY. 



netted-veined : the flowers generally with three organs in each 

 whorl (fig. 456) ; the floral envelopes often all petaloid, or all green 

 or scale-like, rarely with a green calyx and coloured corolla ; seed 

 with an embryo with one cotyledon only. 



The floral formula is, as a rule, P3 + 3 A 3 + 3 G 3, subject to 

 many modifications by suppression, adhesion, <fcc. 



Division I. Petaloidese. 



Monocotyledons, with the floral envelopes consisting of a regular 

 or irregular perianth, of two whorls, both petaloid, or more rarely 

 both herbaceous, sometimes with a green or scaly calyx and a peta- 

 loid corolla (rarely, as in Naiadece, with a scaly uniform perianth, 

 or quite achlamydeous); the flowers mostly perfect, more rarely uni- 

 sexual ; the leaves with the primary ribs parallel, or with a midrib 

 and parallel secondary ribs, or rarely reticulated somewhat in the 

 same manner as Dicotyledons, but with the veins branching at 

 more obtuse angles. 



Exceptions, &c. The greater part of the Orders here associated have a 

 natural connexion in the structure of the perianth (either superior or in- 

 ferior), the syncarpous ovaries, and the perispermic seeds. But a small 

 assemblage of Orders which are included here diverge greatly from the 

 general character, while they differ so much from each other that they 

 cannot very well be separated in the form of one distinct group : these are 

 the Hydrocharidaceae, the Alismaceae, and the Naiadaceae, which agree in 

 the common character of an aperispermic seed : but the first have an in- 

 ferior compound ovary, and seem to approach Bromeliaceae ; the second 

 have more or less distinct carpels, together with a green calyx and coloured 

 corolla, such as occurs in Commelynaceae ; while the third, with uniform 

 scaly perianth or achlamydeous, also apocarpous, in their simpler forms 

 approach in habit to the Araceae. 



Series 1. 



Flower-tube not separate (adherent to) from the ovary. 

 Exceptions, &c. Many Bromeliaceae have free ovaries. 



TACCACE^E are tropical perennial herbaceous plants with tuberous 

 roots and large leaves, somewhat resembling 1 Aracese in habit, but with 

 epigynous, petaloid, hermaphrodite flowers, the perianth of which is 

 tubular ; concealing 6 stamens with petaloid filaments incurved and hooded 

 at the apex ; ovary 1-celled, with 3 parietal placentas projecting more or 

 less into the interior ; fruit a berry ; seeds with fleshy perisperm. The 

 plants are commonly regarded as connecting the epigynous Monocotyledons 

 with the Aristolochiaceae, a Dicotyledonous Order with 3-merous flowers ; 

 they have affinity in habit to the Araceae, and in the flowers approach 

 Bromeliaceae. The watery juices of these plants are acrid; but the 



