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A TEXTBOOK OF THEORETICAL BOTANY 



either herbs or shrubs with entire leaves containing oil glands. In the 

 structure of the flowers they show certain resemblances to the Polygonales. 

 The important families are the Piperaceae and the Saururaceae, which 

 are however sometimes united together. The former is pan-tropical in 

 distribution, but the latter family is restricted to three genera comprising 

 four species distributed over eastern Asia. 



Some authorities regard the Piperales as a very primitive order, deriving 

 it from the Gnetales, and there are some anatomical features to support 

 this view. In Piper nigrum (Fig. 899, Vol. I) the stem contains not only an 

 external ring of bundles from which a zone of secondary wood may be 

 formed but also a number of int'rnal medullary bundles which may be either 

 scattered or arranged in one or two rings. In the genus Peperomia the 

 outer ring of bundles does not become united and the scattered arrange- 

 ment of the medullary bundles recalls that of the Monocotyledons, except 

 that the bundles are not closed. It also resembles closely the flowering 

 stalk of Anemone japuuica (see Chapter XXI). In Peperomia, too, resin and 

 oil-secreting sacs are generally distributed both in the epidermis and in the 

 ground tissue. 



Fig. 1616. — Peperomia peUiicida. A, Longitudinal section 

 of ovule with four-nucleate embryo sac. B, Four- 

 nucleate embryo sac, showing no polarity of nuclei. 

 C, Embryo sac at fertilization stage. {After Johnson.) 



In the structure of the ovules these genera are peculiar. In Peperomia 

 (Fig. 1 61 6) there is only a single integument and the female gametophyte 



