The French pomologists, Poiteau and Turpin,[165] seem to have first made note of the glands in describing peaches, recording their discovery by M. Desprez in the nurseries at the Luxembourg in 1810, after which, for a half-century, French, English and German pomologists regarded them as an infallible means of distinguishing varieties. But, by the middle of the Nineteenth Century, classifiers began to give them up because of their variability on leaves of trees of the same variety or even on the same tree. Even Darwin made note of their insufficiency in taxonomic work.[166] Now, no one familiar with any considerable number of varieties of peaches would attach very great importance to glands in a system of classification. The flowers of peaches are very characteristic, helping to delineate the groups in the several classificatory schemes of various pomologists and being ample to identify not a few varieties. Peach-flowers differ in time of appearance; in length of blooming-season; they may be large, medium or small; pink, rose and rarely white; borne on pedicels of varying length, thickness, color and pubescence; and both the floral and reproductive organs have modifications of their several structures. The size, color and shape of peach-flowers are well shown in the first six color-plates. In some species of Prunus, as some of the plums, the reproductive organs differ greatly in ability to perform their functions, but the blossoms of edible peaches are seemingly always self-fertile and there are less often the mal-formations found in the reproductive organs of some plums. A well-marked correlation[167] between the color in the inside of the calyx-cup and the color of the flesh of the fruit is one of the distinguishing features of peaches. Yellow-fleshed peaches develop from blossoms in which the inside color of the calyx-cup is orange; white-fleshed peaches develop from those in which the color is greenish or greenish-yellow sometimes approaching a very light orange easily distinguished from the dark orange of the other group. Since the discovery of this correlation in the Station orchards by Mr. Charles Tubergen it has been in yearly use and has enabled us to tell a year or two in advance the flesh-color of seedling peaches, since the first peach-blossoms seldom set fruit.