STRUCTURE OF THE APPLE. 425 



studied in the place of the former. This enlarges the opportunity 

 of examination in the fresh state, since cherries or plums can be 

 obtained, more or less ripe, from April, or even earlier, till 

 October, inclusive, and can be readily used for studies in the 

 development of the various tissues, especially of the endocarp in 

 the phenomenon of " stoning," w^ich takes place at a definite 

 period of their growth, during which, for some little while, the 

 young fruit does not increase in size. 



Structure of the Apple. The apple, like the plum and cherry, 

 is a fleshy indehiscent fruit ; while, however, the plum or cherry 

 owes its origin to a free or superior ovary, formed from a single 

 carpellary leaf, the apple arises from an inferior, five-celled ovary, 

 composed of five carpellary leaves. However, having regard to 

 the relations which the nearly allied roses offer, we can assume 

 that the five-celled ovary here is immersed in a hollowed flower- 

 stalk, a so-called hypanthium, or receptacular tube, and is 

 adnate to this ; a view capable of support, however, only on 

 philogenetic grounds. The apple is crowned by five more or less 

 completely-shrivelled sepals, and also by the withered relics of 

 the rest of the floral parts. Surface sections show the epidermis 

 of the apple to be composed of comparatively small polygonal 

 cells, upon which grouping, as a result of development, can still 

 be recognised. The walls of the cells are pretty strongly thickened, 

 their cell-sap either colourless or red. The surface of the epider- 

 mis is covered with a finely granular covering of wax. The small 

 prominences, which are readily visible on the surface of the apple 

 with the lens, are occupied, each in its centre, by a stoma. The 

 tissue under such a stoma is often dead, or else the epidermis 

 is here ruptured, and the wound closed with cork. 



Thin cross-sections show us that the epidermis is strongly 

 thickened on its outer side. Below it lie several layers of tan- 

 gentially-elongated cells, with tolerably thick walls, which, 

 passing inwards, gradually become larger and thinner walled, 

 and at the same time chlorophyll-containing ; otherwise no sharp 

 limit between epicarp and mesocarp is present. The chlorophyll 

 grains are densely filled with starch ; their colour dies away 

 towards the interior of the apple, they at the same time become 

 less numerous ; at length, at a certain depth, the large bladdery 

 cells of the mesocarp contain, besides the delicate peripheral layer 

 of protoplasm and nucleus, for the most part only colourless cell- 

 sap ; the intercellular spaces are here filled with air. Vascular 



