URTICAGEJa. 511 



sometimes cylindrical, filiform, sometimes dilated into a mem- 

 branous cladode, 1 or a plate, cup, or pyriform sac, like the common 

 receptacle of a fig. The flowers are sessile, or pedicellate ; the 

 pedicel has often one or even two articulations, especially in the 

 males. The inflorescence is sometimes naked, sometimes possessing 

 bracts, small and distant, or leafy and involucrant ; free or cohering 

 for a variable distance, they may form a single pair or verticil, or 

 belong to numerous successive generations, corresponding to all the 

 axes of a contracted dichotomous cyme. The type of the flower is 

 variable ; the number of sepals, when present, is from one to five, 

 equal or dissimilar, free or coherent, valvate or imbricate. In the 

 fruit they disappear, or persist, dry and membranous, or thickened 

 and fleshy. The rudimentary gymeceum present in the male flower 

 varies in form with the genus. In female flowers there may be 

 rudimentary stamens below the gynseceum, but they are usually 

 absent. The form of the parts of the gynseceum also varies greatly, 

 according to the genus. The ovary, like the fruit, may be 

 symmetrical or unsymmetrical, with the style at the geometrical 

 apex or some way off it. The middle layer of the pericarp is more 

 or less fleshy ; its surface is smooth granular or tuberculate. The 

 albumen varies greatly in quantity, and may even be reduced to a 

 simple membrane. The form and relative dimensions of the radicle 

 and cotyledons are also subject to numerous variations. 



The constant or nearly constant characters of the order are as 

 follows : simple stipulate 2 leaves, apetalous diclinous flowers 3 grouped 

 in definite cymes, 4 an isostemonous or meiostemonous androceum, 5 

 with a rudimentary pistil in the male flowers, and in the females a 

 unicarpellary gynseceum, with a one-celled ovary ; a solitary, ascend- 

 ing or suberect orthotropous or suborthotropous ovule, with its 

 micropyle ; and finally an inclehiscent fruit. 



The Urticacece also j)resent several histological characters that are 

 constant or very general. AVeddell 6 has shown that the stem of most 



1 Especially in Urtica membranacea (PoiE., ii. [1861], 319^, considering the inflorescence of 

 Diet., iv. 63S), where the axis seems to he the plant as a whole, says that in Urticea it 

 fasciate. forms a repeated polydiopsidal cyme, repeated 



2 In Parietaria alone are the stipules rudi- indefinitely on axillary branches of all ages ; or 

 mentary or absent. an indefinite, indefinitely repeated, sessile axiliary 



3 Usually unisexual, but polygamous in Parie- Cymobotrya. 



twria. 5 Of never more than cue verticil. 



4 GuiLLAED (in Presse St: des Deux Moudes, 6 Monogr., 7. 



