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This testimony may be exaggerated, but it conveys the belief of many that the Nation is a liberal education even to the graduates of our foremost universities. May we send THE NATION to you FREE for four weeks? Subscription Price, Three Dollars Per Year The Nation, Broadway and Fulton Street, New York ISSUED BY The Prudential Provides for Early Distribution of Profits. This policy appeals strongly to the man who wants to protect his family and at the same time realize for himself a substantial and early return on the premiums paid by him. This is done by the apportionment of dividends every five years. The various options at the end of the five-year periods are exceedingly attractive and the experience of the Company shows that business men and others carrying policies upon this plan recommend it highly. At the end of each five-year period, as the dividend is appor- Ist.-Cash. The dividend may be withdrawn in cash or may be applied towards the 3d.-Paid-up Addition to Policy. The The Premiums are Fixed and Never Increase. Policies Issued on the Whole Life, Limited Payment and Endowment plans. The PRUDENTIAL Insurance Company of America Incorporated as a Stock Company by the State of New Jersey Home Office, Newark,N.J. JOHN F. DRYDEN, Pres. Send in this Coupon Without committing myself to any action, I shall be glad to receive free, specimen of Five Year Dividend Whole Life Policy. For $.... Name.... Address........ Occupation....... .Age...... ... Dept 25 If a Specimen Endowment or Limited Payment Policy is desired, specify instead of "Whole Life." BOTANICAL GAZETTE NOVEMBER, 1905 STUDIES OF IRRITABILITY IN ALGAE. GEORGE J. PEIRCE and FLORA A. RANDOLPH. INTRODUCTION. In a recent book on the physiology of plants (13) the statement is made that "when zoospores and other motile and floating spores of sessile plants come to rest, attaching themselves to the substratum, the attachment is effected through means not yet wholly clear. It remains for experiment actually to show that the increased rate and the changed direction of growth in such cases among plants are due to contact, though it seems to be the case in animals" (10). It was with a view to adding somewhat to our knowledge in this direction that the studies here reported were undertaken, first with fresh-water algae, and subsequently with marine. We worked together on the fresh-water algae; one of us worked alone on the sea-weeds; we have gone over all the results together. For the sake of clearness, we may briefly describe the series of events, a small part of which we wish to report in some detail. Zoospores of Oedogonium, Vaucheria, and other fresh-water algae, after escaping from the cells in which they form, may swim about for a considerable length of time. If they are in the light, the direction of their locomotion is influenced by the direction and intensity of the light which falls upon them. This has long been known, though 1 I take this opportunity to express my appreciation of the opportunity of studying, during October and November 1904, at one of the tables maintained at the Zoological Station in Naples by the Carnegie Institution, Washington. I wish also heartily to thank the officers of the Zoological Station for the courtesy which they showed me.-G. J. P. even now far from perfectly understood (7). When the zoospores come to rest, they surround themselves with a cellulose wall. If they come to rest in contact with a solid object, their form changes as well; the part against the solid flattens and adheres to it. Thus a holdfast is formed. The young plant, now sessile, may pass rapidly by successive periods of cell-division and of growth through the subsequent stages of its development. The activities of zoospores, then, are greatly influenced at different times by various agents; the direction of their locomotion is determined by the intensity and direction of the light falling upon them, the formation of cell-wall immediately follows their coming to rest; the growth of the foot or holdfast is proportioned in form and extent to the roughness of the surface with which the zoospore is in contact; and the direction of the first cell-division is probably determined mainly by the light. These last three points we shall discuss in detail. Turning for the moment to the behavior of the non-motile spores of marine algae, such as those of Fucus, Cystoseira, Dictyopteris (Halyseris), we see nearly the same phenomena exhibited. There is no independent locomotion, and hence the transport of the spores from their points of origin to where they are to germinate is not directed by the influence of light upon them, but by water currents. The formation of the cellulose wall, the growth of the foot, and the direction. of the first cell-division (20) are, however, determined by the same influences as those controlling the similar phenomena among freshwater algae. These we hope the following pages will make clear. We shall report first upon the fresh water algae, as it was upon these that we began our work. I. FRESH-WATER ALGAE. MATERIAL AND METHOD. Vigorous plants of Oedogonium, somewhat crowded by diatoms. and other low forms, were found in watering-troughs for horses in paddock or on pasture in the vicinity of Stanford University, California. Many of the plants were growing attached to the sides of the troughs, submersed but near the surface of the water, in some cases fully exposed to the light, in others partly shaded by trees. Other Oedogonium filaments were found attached to dead leaves floating near the surface of the water in the troughs. This water was quiet and fairly clear. The level of the water, tending to be lowered by evaporation or by the draughts of the few horses using the troughs, was automatically maintained by ball-valves, similar to those used in houses. A few other plants, apparently of the same species, were found in a quiet pool in the San Francisquito Creek, growing on stones in comparatively clear water. The material was brought fresh into the laboratory from time to time from mid-September till mid-November, and again from early April till late in May. Since the material did not fruit in our cultures, and we found none fruiting out of doors, it was impossible to determine the species, though we tried to have this done for us. We regret this lack of definiteness in our work. METHOD OF MANIPULATION. Plants brought into the laboratory were placed in an abundance of tap-water in glass dishes covered with a glass plate or loose cap to prevent excessive evaporation and to exclude dust. Small Stender dishes were largely used, since these could easily be placed under the microscope, thereby avoiding such disturbance of the material as transfer from one dish to another would entail. Fortunately for us the water from the tap was from the same source that supplied the horse-troughs, and the creek contains mainly the overflow from the artificial lake which is the general water-supply for the region. When, therefore, our plants were brought in and put into tap-water in the laboratory, they were put into water of the same composition and approximately of the same temperature and degree of aeration as the water of the troughs and the pool from which they had been removed. The behavior of our plants was immediately affected only by those factors changed by the transfer to the laboratory, not by the water, though it goes without saying that the temperatures of the cultures in the laboratory never fell quite so low at night during the winter and spring as that of the water outside in troughs and pools. Cultures were also made in Knop's solution, 1 per cent. and 0.5 per cent. In certain cases we added 10 per cent. gelatine or 0.25 per cent. agar-agar to the Knop's solution, in order to obtain a 24 parts calcium nitrate, I part potassium nitrate, 1 part magnesium sulphate, 1 part potassium phosphate. |