Part 104. Plant Formulas - The Crowfoot Family

104. Plant formulas. We may be helped in summing up what we have learned from our various examples if we express their most significant structural characteristics by means of symbols arranged in a sort of tabular view.

These signs since they apply to the plants as a whole come first in the formula. The letters which follow stand for various parts: L for leaves; l, leaflets; I, inflorescence; i, secondary inflorescence; B, bracts; b, bractlets; S, sepals; P, petals; FA, stamens (filaments with anthers) ; F, staminodes (filaments without anthers) ; CE, carpels (carpellary leaves with ovules, i. e., egg-sac members); E, ovules well developed; e, rudimentary ovules; T, torus; C, carpels ripened into pericarps; E, seeds; G, embryo (germ) ; N, albumen (nutriment).

When the leaves are alternate, as in all the genera except Clematis, this is expressed by L1/1 which signifies that there is a single leaf at each internode. In the exception noted L2/2 means that the leaves are opposite, i. e., two at a node. Palmate nervation is shown by the asterisk *, ternate by the dagger sign †, and pinnate by the double dagger ‡, which, as will be noticed, suggest by their form the arrangement of nerves they each represent. That a leaf is compound is implied by the presence of leaflets indicated by the small l.

In the formulas of Anemone and Clematis this shows that the leaves are but once-compound, while in the Paeonia formula l^1-3 means that the leaves are once to thrice-compound, while l²+ in the Aquilegia and Actaea formulas stands for decompound.

When the inflorescence is of the indeterminate type an inverted comma follows the I as in the Aconitum and Actaea formulas; and when of the determinate type, as in the other examples, an inverted period is used. A solitary terminal flower, as in Paeonia and Nigella, is indicated by I•1. Where, as in Caltha, Anemone, and Clematis, additional flowers may appear forming a cymose cluster, I•1 + is used. When the plant has only solitary axillary flowers like Myosurus the expression becomes I'1. A cymose corymb, as of Aquilegia, is represented by I•'7; while a raceme of the botryose type, as in Aconitum and Actaea, has I", the short and the long oblique lines standing respectively for short and long pedicels. The presence of a small i, as in the formula of Clematis, implies a compound cluster. In this case it is shown to be of paniculate form because of the relatively short pedicels. Where the type and form of inflorescence varies as in Ranunculus, their special signs may be omitted.

The signs ♂, and ♀. As used in the Clematis formula they will be understood as meaning that the inflorescence may consist entirely of perfect flowers (as in the other genera) or may be polygamous.

The presence of bracts more or less like foliage leaves may generally be taken for granted, and so need not usually be expressed in a formula. Bractlets are more often absent, but it seldom matters much for our purpose whether they are present or not, and they rarely need to be taken into account. When either of these organs present noteworthy peculiarities they may be recorded as in the formulas of Paeonia, Caltha, Nigella, and Anemone, following the method for leaves as regards their arrangement, except that in case of involucres only a denominator is used because there is but one whorl. Thus in the formula for Caltha b1/1,0 would read "bractlets alternate or none"; for Nigella b/5,0 means "with five bractlets forming an involucre, or none"; while for Anemone B, b/2,3 means "having bracts or bractlets two or three in a whorl."

The imbricate aestivation of sepals or petals is indicated by two apostrophes, following the S or P, as in the formula of Paeonia; the valvate, by an inverted comma opposed to an apostrophe, as in Clematis.

For each floral organ the number or numerical sign following a letter tells how many of the parts represented are present. The plus sign, +, means "or more," so that 5+ would be read "five or more." The "plus or minus" sign, ±, is to be read "more or less." The algebraic symbol of infinity, ∞, stands here for "many" or "an indefinite number." As a companion sign, oc may be used to mean few. When the absence of an organ needs to be noted a zero, 0, is used. A dash between numerical signs means "to"; thus, 3-5 would be read "three to five"; 0-∞ " none to many." Simply a dash after a numerical sign means "or less"; thus 5- would be read "five or less."

When the numerical signs are in such fractional form as 3/2 or 2/3 (Aconitum formula) it shows that the flower is irregular so far as the organs so represented are concerned; otherwise, the flower is understood to be regular. If the numerator be an odd number it indicates that a single member of the set, more or less unlike the others, is uppermost, as for example, the hooded sepal of Aconitum: an even number, instead, shows that a pair of similar parts is uppermost, as is the case with the staminodes in the same flower.

Unless otherwise indicated the floral organs are understood to be free and distinct. Partial coalescence of parts, as in the carpels of Nigella, is indicated by placing after their numerical sign a small parenthesis: thus, for the example cited CE 5 ±) would be read "carpels five, more or less, partially coalescent below."

There being no indication to the contrary it is also to be understood that the floral organs regularly alternate, and that the anthers

The form of the ovules is shown by a mark placed over their numerical sign, a circumflex accent-mark meaning that the ovule is anatropous. Their ventral position is understood in simple pistils, while in compound pistils like that of Nigella, the single parenthesis after the number of carpels implies that the ovules are on an axile placenta.

When the pericarp becomes fleshy as in Actaea this is indicated by an exclamation mark after the C. When the pericarp is dry, as in Caltha, there is instead an inverted exclamation mark. Indehiscence is indicated by the sign -. When the pericarp dehisces along a ventral suture as in Caltha, etc., the sign - is employed. In all the formulas the expression G-N implies that the embryo is uncoiled within albumen.

The scheme of plant formulas which is here proposed and which will be further elaborated in the following pages, is an extension and modification of the floral formulas used by many botanists. As a sort of botanical shorthand of wide application it is believed that the student will find it not only labor-saving but helpful in grasping plant relationships. After a little use, what seemed strange will have become familiar and a glance will discover important characters that might easily escape notice in comparing equally full verbal descriptions.