4:24 XXXI. THE FKUIT. DEVELOPMENT OF THE FLOWER. 



of very strongly-thickened and lignified elements, the walls of 

 which are traversed by beautifully- branched canals. The history 

 of its development shows that the stone belongs to the wall of the 

 ovary, the pericarp ; that the epidermis of the plum, the epicarp, 

 arises from the epidermis of the ovary ; the flesh of the fruit, the 

 mesocarp, arises from the outer tissue of the ovary, underlying 

 the epidermis ; and the stone, or endocarp, from its inner tissue. 

 The entire tissue of the plum, including the shell of the stone, 

 owes its origin, therefore, to the wall of the ovary. Enclosed in 

 the stone is the seed, consisting of the embryo, a delicate spermo- 

 derm, and a mere remnant of endosperm remaining between the 

 embryo and the spermoderm, so that morphologically the seed is 

 exalbuminous, If we cut it across we can easily distinguish the 

 two cotyledons, lying flat together. A median longitudinal 

 section of the seed shows us, at its base, connecting the two coty- 

 ledons, the hypocotyl of the embryo, with its radicle projected 

 into the pointed micropylar end of the seed, and, between the 

 base of the two cotyledons, the bud or plumule. The embryo, 

 during its enlargement, has absorbed almost the entire tissue 

 of the ovule, up to the very thin spermoderm, from which still 

 arises, quite close to the micropyle, the withered funicle. 



A delicate cross-section through the seed shows us the spermo- 

 derm composed of layers of collapsed cells, and covered on its 

 outer side with rounded cells, thickened either only or chiefly upon 

 the outward bulging sides, and standing either singly or in groups. 

 Surface sections of the spermoderm show us that the thickened 

 projecting elements are single cells or groups of cells of the 

 spermoderm. These have been thickened, and are resistant, 

 while their neighbours remain unthickened, and have collapsed. 

 The pits, abundant upon the side walls, give to these cells an 

 elegant appearance. Where two thickened cells are in contact, 

 the pits coincide. To the epidermis of the spermoderm follows a 

 layer consisting of flattened, irregularly-thickened cells. On the 

 two broad sides of the kernel, a multilamellar layer of endosperm 

 is present, separating the kernel from the spermoderm, but on the 

 narrow sides this is reduced to a single cell layer. <- Two ovules are 

 present in the ovary, of which only one is developed further. 

 Such a free monocarpellary fruit as the plum, with succulent 

 mesocarp, and a stony endocarp, is known as a drupe. ' 



This description of the plum will, apart from unessential 

 differences, serve likewise for the cherry, which therefore can be 



