such that there is a parallel approximation of certain parts of the spirem to form long loops; while other parts, especially those near the center of the nuclear cavity, become knotted and entangled. In the closely contracted and entangled parts of the spirem it is not possible to make out clearly and definitely the arrangement of the chromatin thread, but there is no doubt as to the true nature of the longer loops. Sometimes the loops show a tendency to radiate from the more contracted entanglement of the spirem. The arrangement of these loops is very rarely so regular as figured by FARMER for Lilium candidum (l. c., fig. 9). The parallel sides of the loops are usually twisted upon each other, and the bend of the loop is often, though not always, toward the periphery of the nucleus. It is during this contracted and entangled condition that the thread segments, either partly or completely into the chromosomes. After segmentation the chromosomes begin to contract and thicken more rapidly, and as a result they become more scattered in the nuclear cavity, so that the relation of the two segments toward each other can be readily made out. It is in this and the spindle stage that the chromosomes have been most frequently figured. Those which show the greatest regularity give the impression that they have been formed by a long piece of the spirem folding over in the form of a loop and the parallel sides of the loop twisting upon cach other. Others appear as two parallel rods, which may or may not be twisted upon each other; and in still others the two segments are variously oriented toward each other, as has been figured time and again, and in the greatest profusion, by the different observers.

When one considers the chromosomes in this stage and the longitudinally split spirem of the early prophase, the most natural conclusion is this, namely, that the two parallel rods, or the two segments of each chromosome, of whatever shape, represent adjacent and parallel parts of the longitudinally split spirem; that the spirem thus split merely contracted and shortened, so that the two rather thick halves of each chromosome seemed to owe their thickness to contraction and shortening alone. As a matter of fact, however, the longitudinal split of the thread in Podophyllum becomes obliterated during the formation of the loose and more regular spirem, so that scarcely a trace of the fission can be seen; and, as previously stated

in the foregoing, the spirem contracts and thickens much less before its cross segmentation than has been supposed. The greatest contraction occurs after segmentation, and furthermore the two segments, or rods, of each chromosome do not represent the parallel halves of the longitudinally split spirem, but the approximation of serially distinct parts of the spirem as a whole. Each half of the chromosome is consequently double, resulting from the early longitudinal fission of the spirem, and this fission manifests itself during the meta- and anaphase. It is, therefore, the original longitudinal fission which has been regarded as a second longitudinal splitting. The heterotypic chromosomes of Podophyllum, therefore, are bivalent, and the first mitosis in the pollen mother cells is a "reducing" division. This seems to me now to be the only proper interpretation of the heterotypic chromosomes in Podophyllum. The writer has been reluctant to give up the theory that a longitudinal fission occurs for each mitosis, and he has done so only after a long and careful study of many preparations.

INDIANA UNIVERSITY, BLOOMINGTON.

LITERATURE CITED.

ALLEN, C. E., '05: Nuclear division in the pollen mother cells of Lilium canadense. Ann. Bot. 19: 191-248. 1905.

BERGHS, J., '04: Formation des chromosomes hétérotypiques dans la sporogénèse végétale. I. Depuis le spirème jusqu'aux chromosomes mûrs. La Cellule 21:173-178. 1904. II. Depuis la sporogonie jusqu'au spirème définitif. La Cellule 21:383-394. 1904. III. La microsporogénèse de Convallaria maialis. La Cellule 22:43-49. 1904.

'05: La microsporogénèse de Drosera rotundifolia, Narthecium ossifragum, et Helleborous foetidus. La Cellule 22:141-160. 1905.

FARMER, J. B. and MOORE, J. E. S., '05: On the maiotic phase (reduction divisions) in animals and plants. Quart. Journ. Micr. Sci. 48: 489-557. 1905. FARMER, J. B. and SHOVE, DOROTHY, '05: On the structure and development of the somatic and heterotype chromosomes of Tradescantia virginica. Quart. Journ. Micr. Sci. 48:559–569. 1905.

STRASBURGER, E., '04: Ueber Reductionstheilung. Sitzbr. König. Preuss. Akad. Wiss. 18:587-614. 1904.

RELATION OF TRANSPIRATION TO GROWTH IN

WHEAT.

CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY.

LXXVII.

BURTON EDWARD LIVINGSTON.

(WITH TWENTY-ONE FIGURES)

INTRODUCTION.

TRANSPIRATION being a continuous phenomenon in living plants, and being at the same time readily measurable, it has been suggested by WHITNEY and CAMERON' that here is a criterion for comparing the rates of growth of similar cultures made in different media. It was found at the start that when two cultures of wheat seedlings were prepared, exactly alike except that one was in a good soil and another in a poor, the total transpiration for a period of ten days or more was invariably much greater in the former culture, the difference between the two amounts of water lost being roughly equivalent to the difference between the agricultural values of the soils. It was deemed worth while to investigate this fact more carefully, and the present paper embodies the results of such investigations.

The Russian variety of wheat known as "chul" was used in these experiments. The soil cultures were grown in wire baskets covered with paraffin, such as those described in the paper cited above. For any one series the initial moisture content of all the soils was the same, being about the optimum for plant growth under the conditions of the experiment. The transpiration was determined daily, or at intervals of four days or less, by the method of weighing; and the necessary amount of water was then added to bring the soil back to its original moisture content. The baskets of any series stood side by side in a plant house, being thus subjected to exactly the same changes in temperature, humidity, light, and air currents. Six wheat seedlings were grown in a basket.

I WHITNEY, M. and CAMERON, F. K. Investigations in soil fertility. U. S. Department of Agriculture, Bureau of Soils, Bull. 23. 1904.

CC

Water cultures were grown in black bottles of about 50cc capacity, the seedlings being first germinated in sand and then placed in cork stoppers in the manner described by the authors just referred to. Transpiration was taken by weighing, and the solutions were changed every few days. Otherwise, these were grown under the same conditions as were the basket cultures. Four wheat seedlings were grown in a bottle.

At the end of an experiment the series was photographed, the tops were removed by cutting just above the seeds, the leaf surface was determined, and also the weight of tops and leaves. The determination of leaf surface was made in the following way, which is a modification of that used by previous writers. A plate of glass was coated with dextrin mucilage and the latter allowed to become nearly dry. On this was gummed the wheat leaves side by side, with their edges in contact so far as possible. When the mucilage had become thoroughly dry, but before the leaves had dried appreciably, a photographic print of the leaf outline was made by direct contact. For this the developing paper called "velox" was used; after being developed, fixed, and washed the sheets were squeegeed and dried on ferrotype plates, face down, thus giving perfectly smooth, hard surfaces. The white area of a print so prepared is equal to the area of one side of the leaves whose surface is to be determined. This area was measured by one of two methods, which were found to agree accurately: (1) it was measured directly by means of a planimeter; (2) its area was obtained indirectly by cutting around its margins with scissors and then weighing the white portion as well as the whole sheet. The area of the entire sheet having been first obtained from its dimensions, the required area of the white portion is easily obtained from the known quantities by calculation, assuming that the paper is uniform. The two weights were both obtained at the same time after cutting out the white portion, in order to avoid any errors due to changes in the moisture content of the paper. The uniformity of the latter was tested as follows: four rectangular pieces of velox paper were developed, fixed, washed, and dried as in the actual determination of leaf area. From each of these was deter

2 BURGERSTEIN, A., Die Transpiration der Pflanzen. Jena. 1904. Pp. 24, et seq., and the references there made.

mined, by weighing and measurement, the weight of 154 cm of paper. The results are tabulated below:

Average weight of 154 cm, by all tests, 0.01573; greatest variation from average, 0.00043; greatest variation from average in per cent. of average, 2.7 per

From these figures and other similar ones it appears that this paper so treated is uniform within 3 per cent. of error. Since the planimeter method gives approximately the same results as that by weighing, the two methods can be used interchangeably. The former is the more direct and consumes less time and energy, so that where the instrument is at hand it should be used for this sort of work.

In both soil and water cultures a number of duplicates were often carried through so far as transpiration was concerned. In such cases, owing to the great amount of work involved, the other measurements were made for only one series and not for the duplicates.

The experiments, results of which are recorded in the present