Part 112. The Rose Family - Various Plant Groups

Part 112. The rose family (Rosaceae) as illustrated by the almond (Fig. 31), apple (Figs. 91 I, II), pear (Fig. 92), quince (Figs. 93 I, II), peach (Fig. 94), plum (Fig. 95), cherry (Fig. 96), raspberry (Fig. 97), strawberry (Figs. 98 I-III), and roses (Figs. 148 II, III, 298), is seen to possess many features of floral structure resembling more nearly those of the crowfoot family than of any other family we have studied.

Note in the formulas of Rosa, Fragaria, Rubus, Prunus, Cydonia, and Pyrus, given on pages 408, 409, that the floral envelopes are mostly in fives, while the essential organs are commonly numerous, and that all are free and distinct, except sometimes the carpels, which then, unlike poppy carpels, have axile placentae.

An unusual form of calyx is found in strawberries (Fragaria). Here the sepals have stipules which coalesce in pairs so as to form what looks like a calyx upon a calyx, and is termed therefore an epicalyx.¹ The only other features not before encountered belong to the torus and the fruit. Throughout the family the torus is concave or cup-like, and it is mostly free as in peonies and our examples of the laurel family. In roses (Rosa) it completely envelopes the carpels, and becomes fleshy and bright colored while the pericarps ripen into hard nutlets,² the whole forming a so-called "hip." The strawberry fruit consists mainly of the upper part of the torus,³ much swollen and bearing numerous achenes. Raspberries have the upper part of the torus comparatively dry, and in fruit the pericarps finally separate from it. As these ripen, an outer layer becomes fleshy while an inner layer hardens like an olive stone. A fruit in which the pericarp is thus differentiated is called a "stone-fruit" or drupe.⁴ In raspberries and thimbleberries the little drupes coalesce sufficiently to form a thimble-like mass after they separate from the torus. In blackberries, on the contrary, the little drupes remain attached to the part of the torus which bears them, or in other words, the pericarps adhere ⁵ to the torus, as botanists say of the union of dissimilar parts.

¹ E"pi-ca'lyx - L. epi, upon. S \

² The hardening of the pericarp is expressed in the formulas by two inverted exclamation marks.

³ A small t to represent part of the torus is used in the formulas instead of the large capital.

⁴ Drupe - L. drupa, a ripe olive. Cii7

⁵ Ad-here' - L. ad, to; hoerere, stick.

Such adhesion is represented in the Rubus formula by a bracket placed after the pericarp signs. The bracket is separated by a comma from the preceding signs to show that in this genus the pericarps are sometimes free. Similarly the expression t¡,!, means that the upper part of the torus may be either dry or fleshy in fruit, while C¡¡! means that each pericarp is hard within and fleshy without, i. e., drupaceous.

Each flower of plums, peaches, almonds, and cherries (Prunus) produces but a single drupe, and this has commonly but one seed within the "stone"; though occasionally as in "philopena" almonds both of the ovules develop. It should be noted that neither the "stone" of a peach, plum, or cherry nor the "shell" of an almond is part of a seed, but is the hardened inner layer of the pericarp, enclosing a seed or seeds.

The torus of quince (Cydonia) and of apples and pears (Pyrus), envelops the gyncecium, is adherent to the compound ovary, and both ripen together into the kind of fruit called a pome ⁶ in which the seeds are enclosed in a "core" consisting of dry, more or less parchment-like pericarps, surrounded by the fleshy torus. An adherent torus enveloping the ovary is said to be epigynous,⁷ a term likewise applied to the stamens, or the floral envelopes which it bears; and, indeed, to the flower itself having such a torus. The ovaries of epigynous flowers are termed inferior.

⁶ Pome - L. pomum, an apple or similar fruit. T! C¡ -

⁷ Ep-ig'y-nous - Gr. epi, upon; gyne, pistil. T_w]

A typical formula for the family is shown on pages 408, 409.

The family includes plants of various habit; without milky, colored, or acrid juice, and. lacking reservoirs of volatile oil; but having often fragrant flowers more or less like those of the crowfoot family, but perigynous or epigynous; mostly stipulate leaves, and frequently luscious fruit.