ANGIOSPERM^, DICOTYLEDONES. 



749' 



The Centrospermee are extremely rich in inorganic salts, and in the case o£ many 



of the species soda is extracted from the ash obtained by burning the plants. The 



Piperace^ contain aromatic and pungent substances; the Urticaceee secrete enzymes 



in their stmgmg-hairs (see vol. i. p. 441). The leaves are lobed in Urticaceae and 



Ohenopodiacese, in the rest they 



are undivided and have entire 



margins. In several Cheno- 



podiacesB the cauline leaves are 



squamiform, and assimilation is 



then effected by the green cortex 



of the branches, which are trans- 

 formed into phylloclades. The 



Piperacese are distinguished by 



a peculiar distribution of the 



bundles in the foliage-leaves. 



The lateral strands do not branch' 



off from the midrib in the usual 



way, but are appressed to it and 



can be traced to the base of' the 



lamina. The Urticace^ also, 



particularly the genus Parie- 

 taria, exhibit a peculiar disposi- 

 tion of the bundles (see vol. i. 

 p. 629). The Chenopodiace^ 

 are destitute of stipules, the 

 Paronychiaceae have large mem- 

 branous stipules which protect 

 the foliage -leaves, the Poly- 

 gonacese are distinguished by 

 curious sheathing stipules. In 

 the Caryophyllaceas and some 

 Paronychiaceae the floral enve- 

 lopes are differentiated into 

 calyx and corolla; in Nyctagin- 

 acese, Amaranthacese, and most 

 Polygonacese there is a petaloid 

 perianth, whilst in Chenopodi- 

 acese and Urticaceae there is a sepaloid perianth. The perianth in Nyctaginaceae 

 resembles a corolla most strongly when the bracts are connate and form a 

 sepaloid envelope or involucre, as is the case, for instance, in the Marvel of 

 Peru (Mirabilis Jalapa, see fig. 425). The lowest portion of the perianth in 

 Nyctaginaceae continues to grow after the flower has faded and forms a leathery 

 or woody investment to the fruit (see fig. 425 ^). . In several Chenopodiaceae and; 



Fig. 425.— Nyctaginacese, Mirabilis Jalapa, 



1 Flowering brancli. 2 Fruit inclosed in the persistent base of tlie peri- 

 antii. 3 Longitudinal section tlirougli tlie same; the true fruit is seen 

 within. (After Baillon.) 



