ment by which the four elements and their various compounds have been formed. St. John also speaks of the loro as that through which the world has been made, and so far he seems to be expressing the same idea as Philo. But there is this important difference; that as the loroç is identical with God, it is God as the lóros who has made the world.' Further, the world is not made' in the sense of being 'formed' out of a 'matter' already existing, but is brought into being absolutely.

(3) In Philo, the λóros conceived as the Thought of God is distinct from the λóros as the Word. The latter is the order and harmony of creation and providence. There is no such distinction in St. John. For him the Word is the expression of God himself, and it is to the direct agency of God as the loos that all created things owe their existence. Thus, from whatever point of view we compare them, we find that Philo and St. John, while using the same term, give it an entirely different meaning. At the same time, it is obvious that the metaphor of the Word is only a metaphor, and that the fundamental idea which it is employed to express is that God has revealed himself as He is in the knowable universe, or rather in his Son.

JOHN WATSON.

PLANT SOCIOLOGY.

THERE

ANOTHER CHAPTER IN ECOLOGY.

HERE can be little doubt that the first botanist was the first man. His interest in plants was largely gastronomic; but in his discussions with his offspring, and with the other fauna of his neighborhood, he was fortunate if he had a weapon with many spiral ducts in its vascular bundles. When botanical knowledge had been enriched by the decease of those who ate "not wisely but too well" of the wrong plant, we find that a

ew species were set aside as useful, wholesome, and to be encouraged. The great mass of outsiders were considered with a view to their effect on ailing friends or too vigorous enemies. Later came the laudable attempt to classify all sorts, and so pigeonhole them for ready reference. In connection with this object we find the collecting mania to have developed, until for many years one aim of the botanists seems to have been to reduce. to the condition of more or less libellous mummies, a large number of specimens of every plant beneath the sun.

Then the increased perfection of the microscope gave the laboratory botanist his opportunity, and for the last twenty years we have been trying to get at the true inwardness of every part of every kind of plant. The life processes are also being investigated in the physiological laboratories of all well-equipped colleges, so that we may reasonably hope soon to know the conditions best fitted for the wellbeing of the silent toilers, which so patiently manufacture our food. In connection with this branch of botany there is yet much to be done by all of us who are so fortunate as to have taste and opportunity for walks afield.

We may with profit ask ourselves the following questions : What are the characteristic plants of each well defined plant society;-of the shore, of the marsh, of the swamp, of the meadow, of the forest, of the rocky ridge, of the sand dune ?

What are the conditions to be met and conquered in each environment?

What peculiarities in structure or habit have placed each plant in one of the above societies ?

These are but leaders of an army of questions that suggest themselves, and we may have no fear that our answers will exhaust the subject. This paper will be a brief attempt to suggest a few of the conditions met with in ordinary country districts, and to note a few answers that may be tentatively put forward to meet the innumerable "Why's" with which the subject bristles.

All that we can undertake is to study the characteristic plants of an area with respect to their adaptations. These adaptations are for and against light; for protection; for reproduction,-in connection with the chief factors of environment, which are light, heat, water, soil, wind, animals, other plants, and

topography or drainage. We shall refer to the plants growing under a similar set of the above conditions as a plant society. For convenience, those forming the marsh and swamp society are called hydrophytes; the society of medium or meadow conditions, mesophytes; the dry sand dune or rocky desert group, xerophytes; and the forest plants, hylophytes.

If we visit a small body of open water with muddy bottom, such as a bay or stream, we shall find, first, submerged rooting plants, typical aquatics, for example, Hornwort, Myriophyllum, Water Crowfoots, Beggar Ticks, etc. The conditions which threaten their existence are:-small exposure to light and carbon dioxide, and great liability to destruction from the motion of the water in waves or currents. The dissection of the leaves into cylindrical threads offers the greatest surface possible for exposure to the weak light which penetrates the water, and for the absorption of gaseous food. In connection with the long, flexible, buoyant stems, such leaves also present the condition least likely to offer resistance to water movements. In the second place are the floating plants. Among these will be usually Spirogyra, Cladophora, and Spirodela. Like the rooted plants, these offer little resistance to the movements of the water, and by their thinness afford all parts sufficient light exposure. Thirdly, we find rooted weeds, partly above and partly under water. They may include Pond Weeds, Wild Celery, Bullrushes, Cat-tail, Arrowleaf, Mud Plantain, etc. When these bear submerged leaves they are of the small, or dissected, or very thin types above noted, while the floating leaves are broad and entire. The latter serve to float the blossom for insect pollination.

The genus Potamogeton illustrates excellently the truth that in classification we must attach most importance to the structure. of the flower, and little to the structure of other organs. All other organs are subservient to the support of the flower, and change with the endless variations of condition, with a tendency, however, to become similar in all kinds of plants under similar conditions. The flower being independent of the struggle for food, may remain constant in structure, except as modified for fertilization; and such modification will probably be somewhat uniform within similar latitudes and similar regions of insect distribution. There is a remarkable tendency among plants that are partly

submerged, to modify the vegetative organs into either broad, entire, floating structures, or into narrow, cylindrical, erect leaves or leafstems. When Arrowleaf grows on land or in shallow water, with the leaves completely emerging, these leaves are broad and halberd-shaped; but when growing in deep water with leaves largely submerged, they are narrow; and a perfect gradation exists-coinciding with the extent of leaf emergence,-between this cylindrical petiole-like structure, and the widely expanded leaf.

No one can have looked long at a large growth of water plants without having been impressed with their erectness and narrowness. Rushes, Cat-tails, Blue Flag, Wild Rice and Sweet Flag are all characterized by a similar habit. And this habit persists throughout that most successful and useful family,-the grasses. The Rush occupies a place in two plant societies-the wettest and the dryest-ponds and sand-dunes. Has the habit of growth anything to do with this strange distribution? We may notice that all these erect plants above mentioned are of social growth, reproducing vegetatively, and a good light supply is best secured, in crowded clusters, by narrowness and erectness of members. But protection from extreme heat and light are often required by this style of plant. The cylinder is the plant form which, next to the sphere, gives greatest mass with least surface for evaporation. The same result is obtained by the grasses, which possess to a marked degree the power of reducing their surface in time of great heat by rolling their leaves into cylinders. Again, the conditions surrounding a plant rising above the surface of water are not unlike those endured by the plants of the sand dune. We know that from direct and reflected light and heat, and from the sweep of the wind, the transpiration from such a position must be excessive, hence a thick epidermis and a cylindrical shape may best serve both locations. This same windforce may have also, to some extent, fashioned the narrow ribbon-like foliage.

The zonal arrangement of the plants in and on the margin of ponds is noteworthy. In the deeper water we have White and Yellow Water Lilies, then a circle of the rushes, next Cat-tail and Pickerel weed. A pond of stagnant water will show many of the same characteristics, with the addition of many more floating

plants, as Bladderwort and Riccia. They are here because of protection from water currents and strong wind movements. Although true aquatics, they must float in stagnant water because of the lack of oxygen which is more readily absorbed by moving water, and which would here be used up by the decaying organic matter always present. The Charas, however, remain at the bottom. Are they able to do with little oxygen, and why? We should also note the great plasticity that is shown in the fact of many of the above plants developing entire leaves above water, and dissected leaves below. This is decided just at the time of leaf development, and depends, not on heredity, but on the temporary depth of the water.

Our glance at this extremely interesting society has been directed only toward a few of the conspicuous forms and problems. We must always remember that innumerable company which we estimate per cubic yard of water,-the Diatomaceae, Desmidiaceae, and microscopic algae generally, which form such an. attractive background, and whose simpler forms may aid us greatly in the study of adaptations. We have also ignored that huge group of lithophytes,-the Seaweeds. Why are the more deeply submerged Seaweeds red, and those of shallower water yellow or brown? Why is the under side of the foliage leaves of Nympheae purplish, and the same with the little Spirodela? Why do not Arrowleaf, Pickerel Weed, Water Lilies and Water Plantain develop narrow leaves?

The aid of the microscope is essential to the study of very many of the adaptations, and we find that external conditions produce deep-seated changes. The thin-walled epidermis of submerged plants, lacking stomata, but allowing absorption through all the parts, will be accompanied by corresponding reduction in vascular tissues and in root development. Support by the water will result in small amount of supporting tissue, and often in the development of air cavities. The reduced light results also in a comparatively feeble development of green tissue.

These hydrophytes are the most cosmopolitan of plants, being practically the same on all the different continents. They are of few families, but many in numbers, probably because water gives the most uniform conditions and the greatest chance for dissemination.