422 



BOTANY 



of Polygonum (Fig. 407, "Knot-grass," " Smartweed," etc.), Rumex (Sorrel, 

 Dock), Eriogonum, and several other smaller genera. Of cultivated plants, the 

 Rhubarb (Rheum) and Buckwheat (Fagopyrum) are the most important. 



The Polygonaceae are usually 

 herbaceous plants, but some- 

 times (e.g. species of Eriogo- 

 num) may be woody. The 

 flowers are either diclinous or 

 hermaphrodite, with a regular 

 perianth, which is sometimes 

 brightly colored. The leaves 

 have usually sheathing stipules, 

 and the form of the leaves and 

 the structure of the pistil recall 

 somewhat the simpler Pipe- 

 raceme, with which there may 

 be a remote affinity. On the 

 other hand, the Polygonacese 

 are probably related to the 

 lower Centrospermae, one of 

 the lowest orders of the Chori- 

 petalse. 



SERIES II. CHORI- 



PETAL^E (MESACHLA- 



MYDE.E) 



The flowers in the Chori- 

 petalee are usually hermaph- 

 rodite, and there are two 

 series of perianth leaves, 

 differentiated into calyx 

 and corolla. In some of 

 the lower members of the 

 series, however (e.g. Anem- 

 one, Clematis), there are 

 no petals developed. As a rule, the petals and sepals are four or 

 five in number, but there are many exceptions. 



Among the lower Choripetalee, there are two types of flower, which 

 recall, on the one hand, the flowers of the Apetalse, and, on the 

 other, the apocarpous Monocotyledons, and probably represent two 

 lines of development. These two orders are the Centrospermse and 

 the Ranales. 



In the Centrospermse the flower may be extremely simple, as in 

 Chenopodium or Amarantus. The ovary contains a single basal 

 ovule, and the structure of the flower is very much like that of 

 the Polygonacese or the Piperacese, which they further resemble in 

 possessing perisperm in the seed. In the simpler Ranales (ISTelumbo, 

 Anemone) the flowers have numerous free carpels and stamens, and 



FIG. 405. A, Cytinus hypocistis. Parasitic on 

 the roots of Cistus. B, Rafflesia Patma. 

 Section of the bast of Cissus sp., showing the 

 Fungus-like character of the plant-body of the 

 parasite Rafflesia. (All figures after SOLMS- 

 LAUBACH.) 



