mainly by the direction from which the light comes: the rhizoids are negatively phototropic, the plants positively.

9. As in fresh-water algae, so also in sessile marine algae, the nature of the surface with which the spores come into contact very largely controls the nature of the attachment formed, a rough surface inducing the growth of a large and well-developed holdfast, a smooth surface causing proportionately less growth.

Ic. Though the direction toward which the rhizoids ordinarily grow is determined at first by light, the character of the surface with which the rhizoid comes into contact still more strongly influences the direction of its growth.

11. The direction, rate, and kind of growth of these germinating spores is strongly influenced by contact irritation.

STANFORD UNIVERSITY, CALIFORNIA.

LITERATURE CITED.

1. BALL, O. M., Einfluss von Zug aus die Ausbildung von Festigungsgewebe. Jahrb. Wiss. Bot. 39:303-341. pl. 6, 7. 1903.

2. BESSEY, C. E., Botanical Notes. Science 16:953. 1902.

3. BORGE, O., Ueber die Rhizoidenbildung bei einigen fadenförmigen Chlorophyceen. Upsala. 1894.

4. DAVENPORT, C. B., Experimental morphology. Part II. New York. 5. FITTING, H., Untersuchungen über den Haptotropismus der Ranken. Jahrb. Wiss. Bot. 38:545-634. 1902 et seq.

6. HEGLER, R., Einfluss des mechanischen Zuges auf das Wachsthum der Pflanze. Cohn's Beiträge z. Biologie d. Pflanzen 6:383–432. 1893.

7. JENNINGS, H. S., Contribution to the study of the behavior of lower organisms. Carnegie Institution, Washington. 1904.

8. KLEBS, G., Die Bedingungen der Fortpflanzung bei einigen Algen und Pilzen. Jena. 1896.

9.

Willkürliche Entwickelungsänderungen bei Pflanzen. Jena. 1903. 10. LOEB, J., Untersuchungen zur physiologischen Morphologie der Thiere. I. Ueber Heteromorphose. Würzburg. 1891.

II. MACDOUGAL, D. T., Influence of light and darkness upon growth. Mem. N. Y. Bot. Garden II. 1903.

12. OLTMANNS, F., Morphologie und Biologie der Algen 1. 1904.

13. PEIRCE, G. J., Textbook of plant physiology. New York. 1903.

14.

A contribution to the physiology of the genus Cuscuta. Ann. Botany 8:53-118. pl. 8. 1894.

15. PFEFFER, W., Handbuch der Pflanzenphysiologie. 2te Aufl. 2. 1904.

16.

Zur Kenntniss der Contactreize. Untersuch. Bot. Inst. Tübingen 1:483-535. 1881-5.

17. REINKE, J., Entwickelungsgeschichtliche Untersuchungen über den Dictyotaceen des Golfs von Neapel. Nova Acta Leopold Acad. 50:-. 1878.

18. STRASBURGER, E., Ueber die Wirkung des Lichtes und der Wärme auf Schwärmsporen. 1878.

19. VÖCHTING, H., Ueber den Einfluss des Lichtes auf die Gestaltung und Anlage der Blüthen. Jahrb. Wiss. Bot. 25:149–208. pls. 8-10. 1893. 20. WINKLER, H., Einfluss äusserer Factoren auf die Theilung der Eier von Cystoseira barbata. Ber. Deutsch. Bot. Gesells. 18:297–305. 1900.

THE BOGS AND BOG FLORA OF THE HURON RIVER

VALLEY.

EDGAR NELSON TRANSE A U.

(WITH SIXTEEN FIGURES)

I. The Huron River valley.

PHYSIOGRAPHIC FEATURES.

THE Huron River valley, to the botanical survey of which the present paper forms the sixth contribution, is located in the southeastern part of Michigan. As indicated in fig. 1, the valley embraces parts of five counties.

Throughout, its surface forms are of glacial origin and, with the exception of the immediate borders of the river, have undergone but slight modification since glacial times. Perhaps its most striking topographic features are the rough morainic hills of its upper and middle courses, and the gently undulating plain of its lower course.

The river has its source in west-central Oakland County in Big Lake, 9 miles (14.5km) southeast of Holly and approximately 40 miles (64km) northwest of Detroit. Starting with an elevation of 950 feet (290), after a course, extending for 50 miles (80km) generally southwestward and then for another 50 miles (80km) southeastward, it empties into Lake Erie at an altitude of 573 feet (175) above tide. As is common in areas of glacial deposition, the topography of the drainage basin of the Huron has little of the appearance usually suggested by the term "valley." The upper two thirds of its course is a winding depression among morainic knobs, lake basins, abandoned glacial drainage channels, and sand plains. Here the river is characterized by long reaches and occasional slight riffles. At intervals it broadens into stretches of lake like character, as is illustrated by such bodies of water as Commerce, Taylor, Strawberry, Whitewood, and Bass Lakes, each with an area of one-fourth to one-half a square mile (65-130 hectares). The river margin is usually low and swampy. Its tributaries enter it at every angle, and bring to it the drainage. of hundreds of lakes and swamps. Most of these lakes are small, 1905]

351

occupying areas of an acre (half a hectare) or more, but there are several of considerable size. Portage and Whitmore' Lakes occupy one and one-fourth to one and one-half square miles (325-390 hectares), while Union, Straits, Four-Mile, Ore, Independence, etc.,

FIG. 1.--Map of the Huron drainage basin. The boundaries of the interlobate

moraine are shown by the lines

The boundary between the clay morainic belt and the lake plain is marked by the line

---

cover a fourth to half a square mile (65-130 hectares). A very large percentage of the tributaries lie in flat-bottomed depressions whose surface approximates the ground-water level, consequently producing thousands of acres of swamp and marsh land. Everywhere occur small undrained depressions, some well above the average groundwater level, others containing lakes and bogs. It is also worthy of 1 Not connected with the Huron River by surface drainage.

note that a large part of the surface drained by the Huron and its tributaries, before it makes the great bend to the southeast below Portage lake, is made up of sand and gravel, composing and accompanying the Saginaw-Erie interlobate moraine. It is a region of steep hills, with occasional dry plains, everywhere penetrated by lakes and swamps.

The country which the river next crosses, beyond the great bend, for a distance of 20 miles (32km) is composed of glacial till plains and clay moraines-a belt extending NE-SW, approximately parallel to the interlobate moraine. Here, although the hills are well marked, the slopes are more gradual and the basins broader. The river is bordered by banks several feet in height, and seldom attains a width of 150 feet (50m).

The last 30 miles (50km) of the Huron River traverses a meandering course sunken from 50 feet (15m) at Ypsilanti to 25 feet (7.5m) at Rockwood below the surface of a glacial lake plain sloping gently southeastward from the morainic belt just described, to the western shore of Lake Erie. The soil is here composed of sand, sandy loam, and-in the vicinity of the lake-clay; the only topographic features aside from the sunken water courses being the several beach ridges and dunes marking the successive stages in the lowering of the glacial lakes, forerunners of the present Lake Erie.

There are, then, three natural divisions of the Huron drainage basin: (1) the loose-textured rough interlobate moraine; (2) the clay morainic belt lying to the southeast of it; (3) and the low-lying plain extending to Lake Erie. Each implies important differences in the way of bog formation and provides edaphic factors which determine to a large extent the nature of the dominant forest covering.

PHYSIOGRAPHIC HISTORY.

The history of these topographic features is for the most part bound up with the retreat of the ice at the close of the last (Wisconsin) glacial epoch. A topographic map of the region lying between Lakes Michigan and Erie shows that the morainic hills so characteristic of the Huron basin are part of a belt of similar physiography extending from northern Indiana well up into the "thumb" of lower Michigan (fig. 2). This belt of glacial deposits is directly connected with the