312 



NATURAL IlTSTOnr OF PLANTS. 



Psidium pomiferum. 



rolled. It comprises American trees and shrubs. One has been dis- 

 tinguished under the name of Paivœa, because its receptacular cup, 

 before bearing the calyx, is dilated outwards into a sort of large 



horizontal circular disk. 

 These plants differ little 

 from the Guyavas {Psi- 

 dium), long known by 

 the form of their calyx 

 (fig. 284, 285), which is 

 valvate, gamophyllous, 

 membranous, and which 

 tears at the time of 

 an thesis to release the 

 internal organs. The 

 ovaiy has from two to 

 eight cells in which the 

 ovules, very numerous, 

 are disposed in many 

 series. The fruit is a 

 berry, the pulp of which 

 encloses a variable num- 



Fig. 284. Bud. 



Fig. 285. Long. sect, of fruit. 



ber of seeds, with curved 

 or spiral embryo and short cotyledons. The Guyavas are probably 

 all of American origin, but several have long since been introduced 

 into the tropical regions of the old world. Psidiopsis has been 

 generieally distinguished from them, because the summit of its calyx 

 is dilated into five foliaceous layers. Myrrhinium, a South American 

 shrub, has the leaves, the flowers, and the fruit of a Myrtle, and is 

 immediately distinguished by the almost definite number of its long 

 stamens. There are often only four, that is one facing each sepal ; 

 but from five to eight are not unfrequently observed, because, in 

 this case, there are one or more pairs where in the isostemonous 

 flowers only one stamen is seen. 



Eugenia (fig. 286-289), formerly confounded with the Myrtles, 

 has quite the flower, and differs from them only by one character, 

 viz., that their seeds, ordinarily solitary or few in number, have a 

 large straight embryo, with a short radicle and thick hemispherical 

 cotyledons, placed against each other or even united by their plane 

 surface. Two things differ chiefly in their organization ; the 



