THE FRUIT 375 



consist of a single layer of cells, restricted in distribution, or may form 

 a mass of cells, which enclose the embryo and endosperm. Perisperm is 

 characteristic of many taxa of the higher dicot)'ledons and is prominent 

 in the seeds of the Caryophyllaceae, Polygonaceae, Chenopodiaceae 

 (Fig. 137A), and Phytolaccaceae; in the monocotyledons, integumentary 

 perisperm is apparently unknown, but nucellar perisperm is character- 

 istic of some taxa. 



Perisperm is infrequent in angiosperms as a whole. Both perisperm 

 and endosperm occur in a few families — Musaceae, Piperaceae, Zingi- 

 beraceae, some of the Nymphaeaceae, Chenopodiaceae (Fig. 137A), 

 and related families. But endosperm without perisperm is the common 

 condition. 



Nucellar perisperm is uncommon, because, as the embryo develops, 

 the nucellus degenerates and is commonly completely absorbed, but 

 nucellar perisperm is characteristic of the Piperaceae and Scitamineae. 



Integumentary perisperm is more common than nucellar perisperm. 

 The integuments frequently serve as food storage regions; the tissues 

 that contain the food form the integumentary perisperm. 



The perisperm serves as an accessory nutritive tissue, supplementing 

 the endosperm, which, when present, acts as an intermediary tissue 

 transferring food from adjacent perisperm cells to the embryo. In some 

 families, large amounts of perisperm food seem to be made available 

 to the seedling through the activities of the endosperm — Cannaceae, 

 Caryophyllaceae, Chenopodiaceae (Fig. 137A), Piperaceae (Fig. 138E). 

 The transfer may take place during maturation of the seed, during 

 after-ripening, or during germination. 



The embryo and seedling seem to be nourished at all stages through 

 tissues of the female gametophyte as an intermediary, not directly by 

 the mother sporophyte. 



THE FRUIT 



In angiosperms, a fruit is the matured gynoecium, together, in many 

 taxa, with other floral organs or parts of organs. A fruit has been called 

 a "mature flower," in some respects a good definition, because, at polli- 

 nation, the flower is an immature structure in axis and gynoecium. The 

 pedicel and peduncle may form accessory parts of the fruit. Like many 

 other terms, the term fruit is used loosely; it is applied to the separate 

 carpels of the apocarpous gynoecium (sometimes called fruitlets) — 

 Fragaria — and to fruiting inflorescences — Ananm. Descriptive terms for 

 fruit types are many, but only in part have a morphological base. 

 Classifications of fruits are largely or wholly "artificial"; some classifica- 

 tions have been called "natural," but these make use of such characters 



