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process may be different in different organisms, but I consider it rather improbable in view of the fact that both para- and telosynapes have been described for different groups of plants and animals, and especially since certain "evidences" involved in the argument are not easily observable.

Summing up: contrary to the general belief, so-called end-to-end conjugation does offer an opportunity for interchange between chromosomes at the late thick thread stage in the prophase of maturation division, but at this stage only. If telosynapsis is a universal phenomenon, it would seem that crossing over must take place at the stage here specified. Of course, no morphological evidence has yet been produced for crossing over, and the most that can be said from the present cytological data is that such an interchange is not impossible at a certain stage in the muturation division.

WARO NAKAHARA

DESTRUCTION OF ZOOSPORES OF PLANT DISEASE ORGANISMS BY NATURAL ENEMIES

IN making some motion-picture photomicrographs of the liberation of zoospores from the sporangia of Physoderma zeæ maydis (see Tisdale, Jr. Agr. Res., Vol. 16, p. 137, 1919) the author observed destruction of the zoospores by certain animalcules which are commonly found in decaying vegetable material.

No reference has been found regarding the importance of these natural enemies of the plant diseases which are disseminated by zoospores.

The number of zoospores swallowed by one rotifer (Proales sp.) is remarkable. When the animalcules are abundant there is a speedy disappearance of the zoospores. One infusorian (Keronia sp.) was observed to devour a perfect stream of the zoospores of Physoderma, at the same time increasing in size until it became gorged almost beyond recognition.

In active cultures one may see a field in the microscope filled with millions of zoospores swimming about. In a few hours

large numbers of these have been devoured by the animalcules, which rapidly increase in numbers. A few hours after this one then sees these same protoplasm constituents swimming about not as zoospores but as animalcules. The process of change is so rapid it makes one wonder if there is always cleavage of the proteins and resynthesis or whether there may not be some shorter method of assimilation especially in the unicellar organisms in which the cytoplasms of the infusorian and the zoospore ingested are in such intimate contact.

In starting from dry material collected from cornstalks infested with Physoderma, the animalcules appear first and are on hand for each crop of zoospores.

It would be desirable to determine just how important such animalcules are as natural enemies of those plant diseases which are disseminated by zoospores. Also we should collect data to determine if the destruction of the soil animalcules by excessive liming may not be correlated with epidemics of these diseases.

R. B. HARVEY

U. S. DEPARTMENT OF AGRICULTURE

THE JOURNAL OF MORPHOLOGY AT its annual meeting in St. Louis, the American Society of Zoologists voted to accept the proposition made by Dr. M. J. Greenman, of the Wistar Institute, that in the future the society should assume control of the scientific policy of the Journal of Morphology and elect the editorial board, while the Wistar Institute retained control of the financial management of the journal.

A committee composed of M. M. Metcalf, Caswell Grave and W. E. Castle was appointed to initiate a scientific policy; to nominate an editorial board; to consult with the advisory board of the Wistar Institute and to refer its recommendations for final decision to the executive committee of the society.

This committee on publication and the executive committee and the Wistar Institute have agreed to the following action which accord

gation and independent assortment of factors -has been shown to have a close parallelism with the actual behavior of the chromosomes. The situation is quite otherwise, however, as to the mechanism of crossing over. Morgan is right when he states that "while the genetic evidence is favorable in all essentials to the theory of interchange between homologous chromosomes, it must be confessed that the cytological evidence is so far behind the genetic evidence that it is not yet possible to make a direct appeal to the specific mechanism of crossing over on the basis of our cytological knowledge of maturation stage." Morgan, however, assumes the side-to-side conjugation as a fact. His analysis of data on parasynapsis leads him to the conclusion that the early thin thread stage is most favorable for crossing over to take place. End-toend conjugation, or telosynapsis, according to Morgan, "would have serious consequence for genetics..., for while side-to-side union offers an opportunity for interchange between the paternal and maternal members of a pair, no such interchange could be postulated if end-to-end conjugation took place."

It is the purpose of the present note to emphasize that the process of end-to-end conjugation, at least as described by Nothnagels for a botanical object, and by myself1 for a zoological one, does offer an opportunity for crossing over to take place, contrary to Morgan's statement. End-to-end conjugation simply restricts the stage in which such an opportunity is offered. This can be readily seen from the works of the above-mentioned authors, who describe essentially the following process:

A separate loop or segment of double spireme, whatever the nature of its duality may be, gradually bends and halves of the loop come to lie closely side by side. In the tetrad thus formed there are four longitudinal strands or threads.

It will be seen, then, by telosynapsis, an opportunity is offered for interchange between

Nothnagel, M., "Reduction Division in the Pollen Mother Cells of Allium tricoccum," Bot. Gas., Vol. 61, 1916.

chromosomes at the thick thread stage, but at this stage only, in the manner originally suggested by Janssen in his chiasma type

It must be remembered that the condition of the chromatin threads at the early stage when the double spireme develops is extremely difficult to study minutely and accurately with the method and apparatus at our command. Under such circumstances, any inclination on the part of the observer will have a considerable influence on the interpretation. If one is so disposed, he may consider the condition of the threads as representing the process of pairing up. Dual threads develop out of reticulum at this stage, and that was all I could be sure of. There was certainly no observable evidence of the process of pairing up of two simple threads at least in the stonefly I studied.

On the contrary, the formation of a tetrad or ring by the bending of a loop of double spireme, which appear in haploid number is a clearly demonstrable fact. It is from this ground that I interpret the haploid as being composed of two homologous chromosomes jointed up end-to-end, and its duality as indicating primary splitting. No one has ever seen two chromosomes actually coming into conjugation, but the subsequent bending, reconjugation in side-to-side position, and the ultimate segregation at metaphase, of the halves of the loop is explicable only under the assumption that two chromosomes were united end-to-end in the loop.

Whether I am right in this interpretation or not will be decided by future studies-perhaps in very near future. Detailed comparison of the premeiotic stage with the prophase of somatic mitosis would throw some light on the situation. Also, a careful re-examination of forms (Orthoptera, for instance), in which parasynapsis is customarily claimed to occur, with special reference to the haploid loops in the thick thread stage would help settle the question. Possibility no doubt exists that the

♦ Janssen, F. A., "La théorie de la chiasmatypie. Nouvelle interprétation des cinèses de maturation," La Cellule, T. 25, 1909. theory.

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numbers of these have been devoured ne animalcules, which rapidly increase rumpers A few hours after this one then hese same protoplasm constituents swimg about not as zoospores but as animalLes The process of change is so rapid it one wonder if there is always cleavage the proteins and resynthesis or whether nere may not be some shorter method of milation especially in the unicellar organss in which the cytoplasms of the infusorian and the zoospore ingested are in such nimate contact.

La starting from dry material collected from cornstalks infested with Physoderma, the animalcules appear first and are on hand for each crop of zoospores.

It would be desirable to determine just how important such animalcules are as natural enemies of those plant diseases which are Esseminated by zoospores. Also we should collect data to determine if the destruction of the soil animalcules by excessive liming may not be correlated with epidemics of these diseases.

R. B. HARVEY

U. S. DEPARTMENT OF AGRICULTURE

THE JOURNAL OF MORPHOLOGY Ar its annual meeting in St. Louis, the American Society of Zoologists voted to accept the proposition made by Dr. M. J. Greenman, of the Wistar Institute, that in the future the society should assume control of the scientific policy of the Journal of Morphology and elect the editorial board, while the Wistar Institute retained control of the financial management of the journal.

A committee composed of M. M. Metcalf, Caswell Grave and W. E. Castle was appointed to initiate a scientific policy; to nominate an editorial board; to consult with the advisory board of the Wistar Institute and to refer its recommendations for final decision to the executive committee of the society.

This committee on publication and the executive committee and the Wistar Institute have agreed to the following action which accord

ingly forms the basis for the cooperation between the American Society of Zoologists and the Wistar Institute regarding the Journal of Morphology. The full report of the committee will be published in the proceedings of the 1920 meeting of the society, but on account of the general interest the following summary is presented at this time:

I. That there be elected a managing editor of The Journal of Morphology to serve for a period of five years and that he be eligible for reelection at the expiration of his period of service.

II. That there be elected nine associate editors of The Journal of Morphology; three to serve until

January 1, 1922; three to serve until January 1, 1923; and three to serve until January 1, 1924.

That beginning with the annual meeting of the society at the end of the year 1921, and annually thereafter, there be elected by the society upon nomination, by the same method as is provided for the nomination of other officers, three associate editors to serve for three years to take the places of the three retiring associate editors. That before making nomination of such associate editors, the nominating committee shall consult the board of editors of The Journal of Morphology and also the director of the Wistar Institute and through him the Board of Advisers of this institute.

This is suggested as a matter of courtesy to the institute, not as a matter of necessity, for the election of the editors of this journal shall lie with the society.

That a retiring associate editor shall not be eligible for reelection until after the expiration of one year subsequent to his retirement.

III. That the three incoming associate editors be constituted a consulting committee to visit the Wistar Institute at its invitation and expense, to serve as a means of cooperation between the two organizations.

IV. That the board of editors make annual report to the society upon The Journal of Morphology and any matters of publication that they may wish to include.

V. That the consulting committee, or any of its members, if they desire to do so, may report any year to the society any suggestions or recommendations growing out of their visit to and consultations with the Wistar Institute.

VI. That Professor C. E. McClung be elected managing editor of The Journal of Morphology.

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SPECIAL ARTICLES

A SIMPLIFIED NON-ABSORBING MOUNTING FOR POROUS PORCELAIN ATMOMETERS

SINCE the introduction of porous-porcelain atmometers1 into general use among physiologists, ecologists and agricultural experimenters, it has been realized that one of the most important details of the operation of these instruments in the open depends upon the fact that the porous, water-imbibed surface absorbs water during rains unless special precautions are adopted to prevent this. Mounted on a simple tube, as for laboratory use, these instruments always give negative readings for periods of rapid precipitation. At the end of a rainy day the reading may be considerably smaller than it should be to represent merely the summation of all incre

1 Livingston, B. E., "The Relation of Desert Plants to Soil Moisture and to Evaporation," Carnegie Inst. Washington Publ. 50, 1906. Idem, "A Simple Atmometer,'' SCIENCE, 28: 319-320, 1908. Idem, "Atmometry and the Porous-cup Atmometer," Plant World, 18: 21-30, 51-74, 95-111, 143-149, 1915. Other references are given in these papers.

ments of water-loss by evaporation. The reading may be nil or even negative (entrance of water into the reservoir), in spite of the actual evaporation of significant amounts of water from the instrument during the periods between showers.

It is not feasible to correct for these errors of water absorption, but the difficulty has long been practically overcome by the employment of a rain-correcting, or non-absorbing, mounting for this kind of atmometer when operated in the open during rainy weather. All the non-absorbing mountings thus far suggested depend upon a mercury valve that allows water to pass through the tube freely in the upward direction, but practically prevents movement downward. As soon as liquid water is deposited on the exposed porous surface the surface automatically becomes virtually impervious to water from without, and the precipitation water runs off from the instrument as though it were glazed. When the rain ceases the valve reverses and evaporation soon begins to be registered as water-loss from the reservoir. Various types of mercury-valve mounting have been described, but the Shive form has been most generally used. All these nonabsorbing mountings are relatively expensive, and the least expensive one (Johnston's) involves the use of rubber and requires special care in the installing of the instrument.

A much simpler form of mounting than any hitherto sugested has recently been tested in the Laboratory of Plant Physiology of the Johns Hopkins University. The purpose of this paper is to place the new modification in the hands of those who are interested in atmometry, so as to save them the expense and troubles of the more complicated mountings.

2 Livingston, B. E., "A Rain-correcting Atmometer for Ecological Instrumentation," Plant World, 13: 79-82, 1910. Harvey, E. M., "The Action of the Rain-correcting Atmometer," Plant World, 16: 89-93, 1913. Shive, J. W., "An Improved Non-absorbing Porous-cup Atmometer,' Plant World, 18: 7-10, 1915. Johnston, E. S., "A Simple Non-absorbing Atmometer Mounting,' Plant World, 21: 257-260, 1918.

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The new mounting is very simple. The porous-porcelain piece is mounted in the usual way, by means of a rubber stopper, on the upper end of a glass tube of suitable length and having a bore of about 6 or 7 mm. This tube bears a second rubber (or cork) stopper somewhat below the first, which fits the mouth of the reservoir bottle and closes it completely as far as entrance of rainwater is concerned. The reservoir stopper is not slotted to allow air entrance to the reservoir, but access of air to the interior is allowed through a short, inverted-U-shaped glass tube, one arm of which is longer and penetrates just through the reservoir stopper from without, while the other arm is shorter, is directed downward and terminates a few millimeters above the upper surface of the stopper. This U-tube may be very small and its end may be loosely plugged with glass wool to exclude insects, etc. A water-proof apron over the top of the reservoir may be employed (Livingston, 1908), or other devices to allow air entrance and to exclude rain water may be used.

Thus far we have an absorbing mounting, suitable only for indoor operation or for periods without precipitation. But a very simple and efficient mercury valve is inserted in the upper end of the straight tube, as follows. A tightly rolled plug of glass wool (about 1 cm. long) is inserted in the upper end of the tube, the outer end of the plug is cut off so as to have a flat surface, and it is pushed into the tube until its upper end is about 2 cm. from the top of the tube. Next, a small amount of mercury is placed in the tube above the plug (the mercury column being 5-8 mm. high) and another plug of like nature is inserted above the mercury. The mercury is imprisoned between the two plugs and can not escape, in whatever position the tube is placed.

To install the instrument, the tube is inverted and the end bearing the valve is inserted in distilled water while suction is applied at the other end. Water enters freely through the valve and the tube is nearly filled in this way. Then the porous-porcelain

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