Part 105. The family chain. Having learned the signification of these symbols we are now in position to use the formulas as a ready means of comparing the main structural features of our representative genera to see how they are linked together. Take, for instance, Caltha and Paeonia. If we conceive of a marsh-marigold having a concave torus, a perianth differentiated into calyx and corolla, and pinnately compound leaves, such a plant would be classed as a peony. By these same features, however, it might be distinguished from all the other genera. Therefore, although closely linked with Caltha, Paeonia is placed on a line apart in the tabular view.

Helleborus differs from Caltha chiefly in having the carpels sometimes coalesced and in possessing staminodes. In these respects it is a link connecting Caltha with Nigella which has the carpels always coalescent, and differs from Helleborus only in having pinnate instead of palmate leaves, some of which may be so near the flower as to constitute an involucre, and in consisting of annual rather than perennial herbs.

Aquilegia, with its carpels distinct, is more like Caltha, but differs from both Caltha and Nigella in having the carpels always five, staminodes in two inner sets of five and one outer set of the same number, and in having the leaves ternately decompound.

A monkshood is like a columbine except for irregularity of sepals and staminodes, absence of inner staminodes, indeterminate inflorescence, simplicity of leaves, and sometimes fewer carpels.

All the above genera agree in having numerous ovules, all of which may become seeds, contained in several or many carpels which become dry and dehiscent in fruit.

In Actaea the carpels are reduced to one, which becomes fleshy and indehiscent in fruit; the staminodes may be fewer, both they and the sepals are regular; and the leaves areternately decompound: otherwise the genus resembles Aconitum.

Passing now to Anemone we find its most striking differences from Caltha and the other genera already described to be the imperfect development of several of the ovules in each carpel, the ripening of only one ovule, the indehiscence of the fruit, and the possession of an involucre of two or three bracts. In these respects it forms a link between our type genus and Clematis where the rudimentary ovules are commonly fewer, and all the leaves (like the bracts in some species of Anemone) are opposite.

A still further divergence in Clematis appears in the occasional imperfection of the flowers, the valvate aestivation of the sepals, the ternate or pinnate nervation of the leaves, and the climbing habit and woody stem sometimes developed.

In Ranunculus we find a still further reduction of the ovules; an invariable presence of both essential organs and staminodes; imbricate aestivation of the sepals: alternate, palmate, simple leaves; and sometimes annual duration: thus being in some respects more nearly like Caltha, while in others it is more divergent.

Finally, an extreme of divergence by reduction or simplification is reached in the mouse-tails which may be regarded as annual crowfoots with only about five stamens, staminodes, and sepals, bractless, solitary flowers, and leaves with unbranched or obscure nervation. It may seem a long way from such plants to peonies; but, as we see, there are intermediate links binding them pretty closely together.

As the student examines other members of the same family he will find that they may be readily interposed as links in the same chain with those already studied. Indeed, the transitions will appear less abrupt than between the few examples to which we have confined ourselves. His experience will be much like that of a botanist with forms newly discovered. He compares them with the forms already known and links them with those which they most nearly resemble. Thus link by link are family chains forged in botanical systems. As in the present case, the chain may branch, and it might be questioned whether it would not be better to regard the branches as separate families. That depends upon how close the linkage appears to be, and as to that the judgment of experts may differ. In any event the definition of any family properly follows the attempt at natural grouping, and may require revision with advancing knowledge or change of view. Such changes in classification the history of the science illustrates; yet progress is in the direction of stability, and certain chains, having held from the first, bid fair to endure. The integrity of the Ranunculaceae, for example, seems assured in spite of the wide divergence of its extreme forms and in spite of the difficulty of defining its limits.

We have now to define the family as best we can. The generic formulas will help us to a formula for the family and this in turn will lead us to our definition. Taking the prevailing characteristics of each part as typical for the family, and neglecting the less significant exceptions to the general rule, we may express a generalized view of the salient features as shown in the formula of Ranunculaceae on pages 404, 405.

The only invariable features here expressed are the anatropous ovule and the uncoiled embryo surrounded by albumen, and these as we shall see are common to a number of other families. But, as we shall also see in comparing the Ranunculaceae with other groups, it lacks features which they possess.

Taking into account all the facts we have learned, the crowfoot family may be described as consisting of herbaceous or rarely woody plants, never trees, without milky juice, oil or other secretions in special reservoirs, but with a mostly colorless and odorless sap which is generally acrid, and in some cases renders the plant poisonous to eat or to touch; leaves mostly palmately branched, or at least palmately ribbed; flowers mostly regular and perfect with the parts free and distinct (with rare exceptions); sepals commonly five, generally petaloid; petals rarely present, often replaced by more or less petaloid staminodal nectaries of widely differing forms; stamens generally numerous; anthers dehiscing by slits; pistils almost always simple, numerous, few, or rarely solitary; ovules anatropous, many, few or solitary, sometimes rudimentary; fruit follicular, capsular, achenial, or rarely fleshy; the seeds with hard albumen surrounding a minute uncoiled embryo. Or, if we disregard all that is untypical, it may be said that whenever we find an herb with the juice colorless and scentless, the flowers having all their parts distinct and free, sepals about five, and essential organs numerous, we may be tolerably sure that our plant is one of the crowfoot family, although some departure from these characteristics would not necessarily exclude it from the group.