condition of complete parasitic phenogams, but those which are only partially normal supplement their honest gains by theft. They are all robbers, and obtain new organic substances from their hosts by methods which resemble grafting, budding and leeching, respectively. In the first two cases mentioned the embryo of the parasite is thrust into the living tissue of the host from which the resulting parasitic plant draws its nourishment, much as do the bud and scion in cases of budding and grafting. In the other case special organs, namely, haustoria, are developed as instruments of robbery. These organs serve to draw new organic substance in liquid form from normal plants, and they are as indispensable to the parasite which possesses them as are roots to normal plants. They are produced as small outgrowths from different parts of different parasitic species, sometimes upon the roots and sometimes upon the stem and branches. They are of wart-like, discoid, globular, or more or less irregular form, and are sometimes single and symmetrical, but oftener in groups or clusters and shapeless masses. When single they are sometimes sessile and sometimes terminal on slender pedicels. They attach themselves by their free surface to the host, and so burrow into its subcortical and subcortical tissues that the growing cells of both plants are intimately commingled. Acting like suckers, they withdraw in liquid form the new organic substance which the host had prepared for its own use, much as a leech extracts blood from its victim. The haustoria of parasites are comparable with roots of normal plants because, like roots, they are the instruments by means of which the plants obtain necessary supplies, but true haustoria are not roots nor morphological representatives of them.

The foregoing remarks apply mainly to the general characteristics of the parasites as compared with saprophytes, symbionts and normal plants. The special characteristics of the parasites are grouped and briefly summarized in the following synopsis. In remarks which follow each synoptical statement some of the more con

spicuous of those extraordinary habits which members of the various groups possess and which have become constant and hereditary will be shown. Many of those habits are of wonderful character, and one almost feels that he is dealing with sentient beings of great cunning and lawlessness rather than with vegetal forms.

The phenogamous parasites are so aberrant as regards both their structural and vital relations to other plants and to one another that it is difficult to classify them. Indeed, there is no logically recognizable correlation of any of the parasitic characters of the species in question with those which pertain to systematic classification. The following synopsis, prepared for the present occasion only, embraces seven groups the characterization of which is, so far as practicable, based upon the manner of parasitism of the members of the respective groups and upon the peculiarities of their life history, especially that phase of it which pertains to germination.

GROUP I

Seeds germinate upon the ground. Embryo differentiated into cotyledons, radicle and plumule, like normal em

FIG. 1. Diagrammatic pen bryos. Like normal plants

sketch, showing the position of haustoria at the places of contact of roots of the parasite and its host. The haustoria are represented by small circles, which are, however, proportionally much larger than natural size.

also those of this group produce chlorophyl. A part of their roots are attached by sessile haustoria to roots of other plants, from which they obtain ready-made organic substance in liquid form, and a part of them obtain food-sap from the soil in the normal manner. Therefore their parasitism is only partial. Examples: Euphrasia, Pedicularis, Castilleja and many others.

The parasitism of the members of group I, which are

mostly perennial herbs, is confined to limited underground pilfering. It is the simplest form of phenogamous parasitism but it is as persistent and hereditary as are the more complex forms, and it is practised by a large number of genera and species which have numerous near normal relatives. Because they have normal roots and leaves and produce chlorophyl they begin life with the ability to procure an honest living, but they seem to be unable to resist their inherited parasitic inclinations. The development of haustoria at the points of contact of their roots with roots of other plants begins after their germinative birth from a normal embryo and an early stage of full self-support obtained from the soil; but so firmly fixed is the habit of pilfering in these plants that when they have been experimentally forced to live honestly in good soil, but beyond the reach of roots of other plants, they have ceased to thrive, as if they were insufficiently nourished.

GROUP II

Parasites attached to the stems and branches of woody hosts upon the bark of which the seeds germinate, being affixed there by their glutinous covering. Embryo differ

A

FIG. 2. Pen-sketch of a branch of Viscum album, the Old World mistletoe; much reduced in size. A. Diagram showing the mode of attachment of the parasite to the host by the sinkers.

entiated into cotyledons, radicle and plumule, and the plant consists of both epitropic and apotropic portions. The latter is differentiated into stem, branches, leaves and fruit, as in normal plants. The leaves, and also the bark of the stem and branches, contain chlorophyl which is produced by the plant itself. The parasite is attached

to the host by "sinkers" which consist of specially modified, but true, rootlets, although in function they simulate the haustoria of other parasites. The sinkers penetrate the bark of the host and obtain nourishment for the parasite from the growing tissues beneath it, much as food-sap is obtained from the soil by normal plants. The parasitism is complete. Examples: The mistletoes.

The members of group II are perhaps the most generally known, at least by name, of all the phenogamous parasites. The family

to which they belong,
the Loranthaceæ, is a
large one, and some
of its members differ
considerably from the
typical forms of mis-
tletoe. Only Viscum
album of the
of the Old
World, and Phora-
dendron flavescens,
of the New, however,
are chosen to repre-
sent group II on this
occasion. These mis-
toes differ from the
members of all the
other parasitic groups

in being perennial woody parasites upon woody hosts, and also in their method of parasitism. That method is peculiar because it simulates grafting, because morphologically its "sinkers" are true rootlets and not haustoria, and because the passage of sap from host to parasite is by those rootlets and not through such harmoniously joined cells as are formed between the graft and its stock. Mistletoes have been known to become parasitic upon other mistletoes, but in their choice of a host they usually give preference to trees that are not botanically related to them. Their structure, both embryonal and mature, is so nearly normal that one might believe them capable of

leading an honest life in the soil, but so firmly is their predatory habit established by heredity that they never do so. Their seeds will germinate successfully only on the bark of living trees, and their embryos, although structurally perfect, are evidently unable to develop in the soil. When germination of the seed begins the radicle pierces through the dry bark of the host as if driven by some extraneous force; and it sometimes enters the bark of a branch from its under side, showing that gravity is not that impelling force. It lifts the strong bark by its increment beneath, and sends the sinkers into the growing layers. The cells of those layers and the cells of the sinkers become vitally commingled much as do the somatic cells of the scion and stock in common grafting, but not quite so harmoniously. This parasitic root-grafting is remarkable because the parasites and their usual hosts differ from each other in botanical relationship far more than do any scions and stocks that can be artificially grafted with success.

Because the mistletoes obtain full nourishment from their hosts their parasitism is complete, and yet, unlike other completely parasitic phenogams, they produce chlorophyl in their own tissues. The production of chlorophyl by the mistletoes is apparently due to the fact that they have retained morphological representation of true roots, notwithstanding their parasitism. While the mistletoes. have retained more of the structure and functions of normal plants than have other completely parasitic phenogams, their draft upon the vitality of their hosts is great, and it doubtless would be more apparent if the latter were less vigorous.

GROUP III

Seeds, having the embryo differentiated into cotyledons, radicle and plumule, germinate upon the ground and there produce plants which begin to grow in the soil in the normal manner. By their earlier roots they are partially parasitic after the manner of group I, but, suddenly, the whole plant becomes epitropic and enters the soil bodily by burrowing, much as does the peanut pod