486 NATURAL HISTORY OF PLANTS. 



cells. The axis of the stem is occupied by close-packed elongated 

 elements, which, perhaps, represent a woody zone, or rather a pith with 

 its cells drawn out. 1 The leaves are remarkable for that the paren- 

 chyma with chlorophyll is only superficial, surrounding a very large 

 central canal, here and there interrupted by thin transverse cellular 

 septa. 



Affinities. — The Piperacea are especially close to Urticacea, of 

 which they often have gynseceum, placentation, and ovule, and some- 

 times, as in Laurea, habit, foliage, and inflorescence. But their 

 perianth is different, save in doubtful cases, such as Hedyosmum, 

 where the ovary is quite inferior, and Ceratophyllum, so distinct in 

 all other features. Moreover, Urticacece lack the double embryo of 

 most Piperacece, their aromatic odour, and the leafy embryo of Cerat- 

 ophyttum. All the secondary groups that were formerly placed with 

 Piperacece in Urticinece, such as Morea, Artocarpece, Vlmacece, Canna- 

 binece, &c, have a gynaBceum of more than one carpellary leaf and 

 anatropous ovules, not to mention the characters of the habit and 

 male flower. Through Chlorantkcce and Ceratophyllece this order 

 seems allied to Hippuridea, and, as some have thought, to Loran- 

 thacear. But this last affinity, and that to Polyyonacece, Sakolacea, 

 &c, seems to us less evident, for all these types have a pluricarpellary 

 gynaeceum, with truly central placentation. Piperacece are, in the 

 first place, inseparable from the Nettles. Next, by their more 

 complicated types, they come very close to Datiscece. If we compare 

 Gymotheca and Tetrameles we shall see that their floral organization 

 is fundamentally the same, except that the latter has a perianth. 

 This closely connects Ur/icacea and Saxifrayacea, which are also 

 linked by Myosurandrece, for, as we have already shown, Myosurandra 

 has the branches, opposite leaves, odour, and inflorescence of Chlor- 

 antlius, the sheaths and stipules of Hedyosmum, the naked flower of 

 the Piperea and Saurtcrece, the free carpels of several of the latter, 

 with a ventral placenta, and differs in no absolute character but its 

 anatropous ovules and single albumen. 



1 Spiral vessels have been described in these plants, but we have been unable to find them. 



