96 
PLANT MORPHOLOGY. 
the poppy, or be developed into hairs, as in vanilla and 
orange, or be more or less obliterated, as in acbene-like 
fruits, or be modified to sclerenchymatous elements, as 
in drupes. 
The middle layer, which is composed of parenchyma, 
may contain organized cell-contents, starch, sugars, 
calcium oxalate, coloring principles, alkaloids and 
other principles, and it may also have oil-secretion 
cells, as in cubeb, or oil-secretion reservoirs, as in 
orange and the fruits of the Umbelliferse, in the latter 
of which they are known as vittae; milk vessels some 
times occur, as in poppy; a collencliymatous layer is 
sometimes developed beneath the epidermis, as in cap- 
sicum; in some cases sclerenchymatous cells may he 
present, as in pimenta; and in still other instances the 
entire pericarp may be made up of stone cells. 
III. THE SEED. 
The seed may he defined as the fertilized and de- 
veloped ovule. The seeds of different fruits vary in 
number as well as in size and shape. In form they 
correspond to the ovules; in size the} 7 vary from about 
1 millimeter, as in the poppy, to 10 or 15 centimeters in 
diameter, as in the cocoanut palm. Seldom ai’e all of 
the ovules of the pistil fertilized, hence the number 
of seeds is usually less than the number of ovules. 
After the fertilization of the egg-cell certain changes 
take place in the embryo sac: at one end the develop- 
ing embryo becomes attached to the wall by a stalk ; 
the nuclei, lying in a mass of protoplasm around the 
wall, divide and re-divide; the large vacuole in the 
center becomes filled with a watery or milky fluid, 
and later the nuclei, with portions of the protoplasm, 
may be inclosed by a cellulose wall and become 
permanent cells, in which the embryo is embedded. 
