of the eggs of this pest, such as may guide the farmer in his sowing or planting so that the young plant may escape the ravages of the young insects.

INFLUENCE OF TEMPERATURE AND MOISTURE ON GERMINA

TION.

The influence of temperature and moisture on the sprouting of seeds has been studied by Sturtevant at Cornell University (Agr. Exp. Sta., Bull. No. 7), with results generally confirming those of De Candolle. Sprouting occurs better with a uniform than with a variable temperature, so that the method of Quetelet, which requires us to take account of the squares of the temperatures, is no better than that which considers the simple temperature. The rapidity of sprouting diminishes with the decrease of temperature. The percentage of seeds that sprout does not depend upon the uniformity of the temperature. Sprouting takes place more rapidly in a rather dry soil, but a decidedly wet soil is injurious. By soaking the seed before planting it, the interval between planting and sprouting is diminished, but not between soaking and sprouting; hence the total time required and the total percentage of sprouting seeds is not much affected by the soaking. The exposure to light during germination retards some seeds, but does not affect others. Actual planting in the field may give 50 per cent less germinations than given by similar seeds planted in experimental pots under control.

INFLUENCE OF LIGHT AND HEAT ON GERMINATION.

Pauchon (1880) summarizes the results of the studies of many authors on the relative influence of light and heat on the germination of seeds and the growth of plants. The following section is condensed from him:

Edwards and Colin (1834) state that in their day little was known as to the influence of light and air on the green matter and on the respiration of plants; since then, however, it may be considered as established that the life of a plant varies in proportion to the adaptation of the plant to its surroundings. The study of the influence of light may be said to have begun with Lavoisier, who thought that the light directly combined with certain parts of the plant producing the green leaves and colored flowers, and that without light there could be no life. Similarly Moleschott (1856), at Zurich, affirms that in general everything that breathes or moves draws its life from the light of the sun.

Boussingault (1876), controverting a statement of Pasteur, maintains that the growth of mushrooms and mold in the dark is not an exception but a confirmation of the general rule, and that if the solar

light should be cut off both the plants having chlorophyl, and also the plants that do not have it, would disappear from the surface of the globe.

Berthelot, in his essay on the mechanics of chemistry as based on thermochemistry, shows that the action of the light is demonstrated by the formation of complex chemical effects, isomeric changes, and more complex reactions. For instance, the combination of free oxygen is stimulated in a great many cases by the action of light, as is shown by the bleaching of fabrics of any kind exposed to the air and by the oxidation of volatile oils. All the oxidizing in reactions brought about by the action of light is exothermic-that is to say, there is a loss of energy in the transition from the compound body to its elementary components and a disengagement of heat. The light plays the rôle of a determining agent. On the other hand, when a complex body is built up in the cells of a plant, by drawing in elementary bodies from the atmosphere and soil, the reaction is endothermic, and solar heat is absorbed and rendered latent in the plant.

Sachs, Wiesner, and Mikosh would seem to have established the principle that the formation of the green matter of a plant is not dependent wholly on the light as such, but also demands a certain temperature, varying between 0° and 35° C., for the various plants of Europe. They show also that an increase in the temperature of the atmosphere, with equal increase of light, increases the rapidity of the formation of the chlorophyl up to a certain maximum temperature, and that in proportion as the temperature departs from this favorable maximum, either above or below, the formation of the green matter becomes less and less active, until when the limits 0° or 35° C. are exceeded it ceases altogether. But the temperature most favorable for the formation of chlorophyl under the action of light has but little connection with the temperature that promotes the further action of the chlorophyl after it has been formed within the plant. Thus Timiriazeff (1880) shows that the activity of the chlorophyl consists in the absorption of certain radiations; but in order that these radiations may act it does not suffice merely that they should be absorbed; it is further necessary that there should be a very consid.erable intensity of heat, in order to furnish to the chlorophyl the definite number of calories necessary for the decomposition of the carbonic-acid gas taken in from the atmosphere.

In general, under ordinary conditions light is indispensable to the formation of chlorophyl. To this general law there are a few apparent exceptions, as follows: The embryos of the genera Pinus and Thuya have their cotyledons colored an intense green at the moment of germination, even when they have been or appear to have been completely deprived of the action of light. So also with a certain number of phanerogams in which the embryo is protected by thick

integuments; finally, the fronds of certain ferns have a green color, even when they grow in complete darkness. With regard to the seeds of Acer, Astragalus, Celtis, and Raphanus, it has been shown by J. Böhm that when they germinate in darkness they do not acquire any green color; Flahault (1879) has obtained the same result for the seeds of the Viola tricolor, the Acer pseudoplatanus, and the Geranium lucidum. Similarly as to the other seeds above enumerated the studies of Sachs and Flahault render it probable that in most cases there was stored up in the seed certain reserve nutrition, which reserve, originally formed under the action of light, can subsequently in the act of germination temporarily replace the further direct action of light. It would thus seem that in no case can dark heat truly replace the action of sunlight.

On the other hand, light can replace heat in the process of vegetation. This was first shown by De Candolle, and a striking illustration is quoted by Moleschott (1856), who shows that by the influence of light during the resplendent nights of the polar regions the harvests ripen in a short time, while many days of our autumn heats in lower latitudes scarcely suffice. It is the quantity of light and the quality of the radiations that these plants receive that enable certain cereals, such as barley and oats, to be cultivated as far north as 70° of latitude. The observations of Schleiden on the potato, of De Candolle on the radiola, and of Haberlandt (1866) on oats, show that there exist decided differences in the quantities of heat necessary to the development of different species of vegetables under different latitudes, and that the most important cause of these differences is the quantity of light which these plants receive. De Candolle, in his botanical geography, says the effect of light is shown in the northern limits of certain species; thus the radiola is perfected by a total supply of heat represented by 2,225 day-degrees in the Orkneys at 59° north, but by a total of 1,990 day-degrees at Drontheim, latitude north 63° 25′; the difference (235) corresponds to the fact that the longest day is 14 hours longer at Drontheim than in the Orkneys, which increased sunlight enables the plant to complete its growth better under the same temperature.

Wheat furnishes a still more striking example. It begins to vegetate when the temperature in the shade is about 6° C., and observation has shown that it requires the following day-degrees to ripen: At Paris in 138 days, total shade temperature 1,970° C.; at Orange, 117 days, total shade temperature 1,601° C.; at Upsala, 122 days, total shade temperature 1,546° C.; at Lynden (North Cape), 72 days, total shade temperature 675° C. Or, if we use, not the shade temperatures, but those of a thermometer exposed to the full sunshine, as is done by Gasparin, then the above figures become at Orange, 2.4681 day-degrees; Paris, 2,433 day-degrees; Lynden, 1,582 day-degrees.

These remarks of De Candolle with reference to germination are equally applicable to the whole period of growth of the piant.

As to the method of calculating the sum total of temperatures De Candolle found that it may be conducted in two ways, either by adding together all the mean daily temperatures above 0° C. or by omitting the useless degrees and adding all the others. This last method would seem to be the most logical, but can rarely be employed, owing to our ignorance of that minimum temperature below which all must be omitted. On the other hand, if we consider that a plant which vegetates between 10° C. and 30° C. has a maximum at 20° C., and if we seek the coefficients of growth corresponding to each successive degree of temperature, we find, as Boussingault has shown, that these coefficients vary for each degree as we depart above or below the temperature most favorable to vegetation.

Similarly De Candolle (1865) has shown that near the minimum and near the maximum temperatures the rate of germination is more difficult, and therefore slower, than at the intermediate or best temperatures; consequently, both in germination and in subsequent vegetation, it is necessary to recognize the fact that calculations of the sums of heat in connection with the study of the geographical distribution of plants are complicated with hypotheses and many sources of error.

Schuebeler (1862) shows that cultivated plants in northern countries have more highly colored flowers, larger and greener leaves, and larger seeds, which are more highly colored and richer in essential oils, than those of southern regions. Bonnier and Flahault (1878) have shown the same facts for uncultivated plants. Both these authors attribute this result to the prolonged action of sunlight, and the latter shows that the variations are exactly proportional to the duration of sunlight. In Flahault's more recent observations he shows that there must necessarily exist a relation between the quantity of carbonic acid decomposed and the quantity of carbonaceous matters formed by the plant, and that in general the sunlight has a very remarkable influence on vegetation since it compensates in a large measure for the deficiency of temperature.

It is, furthermore, to this influence of light that Pauchon attributes the singular fact that plants cultivated in high latitudes are endowed with a vegetating power greater than that of southern countries, so that when transported to the south their seeds ripen sooner than those of the southern plants. This subject has been especially studied by Tisserand in his memoir on vegetation in high latitudes, as cited by Grandeau in his work on nutrition of plants. According to Tisserand a plant behaves in northern latitudes as a more highly perfected machine and one that performs better than southern plants. In regions where it has neither time nor heat it gains in activity and

in the speed with which it perfects its own growth. It seems to Pauchon that we may properly interpret this phenomenon if we admit that a seed transported from the north to the south finds itself in climatic conditions more favorable to the development of the embryo which it contains and of the plant which is to follow. What the action of light loses in duration in proportion as we move toward the equator it gains in intensity. It may be that the cause of this increased activity is due to the larger size of the northern seeds or to their greater richness in the essential oils. Pauchon thinks that the embryo of such a seed should not be compared to a more perfect machine; it is rather an identical machine, but better nourished by the reserve of combustible and nutritive material in the perisperm. Possibly the abundance of essential oils contained within the seed contributes to furnish to the embryo in northern countries the materials for the oxidation that is necessary in order to maintain its temperature during germination and to struggle against the severity of the climate.

Tisserand (1876) has shown that the rye cultivated in northern Norway has not the same chemical composition as that of France and Algeria, and that in general, as we go northward, or as we rise above the level of the sea, or as the temperature lowers without diminishing the quantity of light, we see the starch in the grain increase relatively to the nitrogenous components. Wheat grown at Lynden (North Cape) has a smaller proportion of gluten than the wheat of France, and the latter less than the wheat of Africa. On the other hand, barley raised at Alten, on being sown at Vincennes on the 7th of April by Tisserand, was ripe on the 18th of June, or thirty-seven days in advance of French barley, so that in order to mature it required a sum total of heat far less than the French barley. The reverse is true when southern grains are carried north and sown in colder climates. Therefore, as Marie-Davy has remarked, plants become acclimated more or less rapidly according to their own nature and the extent of the climatic variations that are imposed upon them; the climate produces in them a functional change which corresponds to an organic change the nature of which often escapes our observation. It is therefore not necessary that each phase of vegetation should correspond to a constant sum of heat in very different climates. That which it is important for us to know is what are the limits between which this sum total can vary, for the same species of plant under different climates.

The general fact that the quantity of nitrogen contained in the seeds increases as we approach the warmer climates leads to the hypothesis that the formation of albuminous reserves within the seed takes place in proportion to the temperature, and that the formation of starch and other reserves takes place in proportion to the duration