Chapter VII.

MISCELLANEOUS RELATIONS.

RAPID THAWS.

The following extracts from a report for 1889 of the department of the interior of the Canadian government shows the influence of the change from warm to cold weather not only on forest trees but on other plants:

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Considerable attention has been paid to this subject during the past year, and there has been urged on the department of agriculture the desirability of the establishment at some point in the southwestern portion of the Northwest Territories of a farm or garden for conducting experiments on this line. Failure in tree culture so far as tried seems to be owing not to the severity of the winters, nor to the droughts of the summers, but to the winds. Those in the winter known as chinooks," which cause the sap to rise and the buds to swell, being followed by a lowering of the temperature (in some cases very rapid), prove destructive; and during the summer there are often high, dry, hot winds which blow continuously for several hours and which seem to dry up the young trees. By planting in close clumps the native trees which will grow (cottonwoods and others), and among them those ornamental trees which are so much to be desired, these difficulties will probably be overcome, and in time it will be found what ones are best suited to the district.

The great difficulty which at present impedes the cultivation of large plantations of forest trees in Manitoba and the northwest is climatic. In early spring, delightfully soft, balmy days, something like the maple-sugar weather in Ontario and Quebec, awaken the young trees to life and cause the sap to run; but then suddenly a terrific blizzard from the north and northwest comes down and freezes up the sap and destroys the trees. Professor Saunders is now engaged in experiments with a view to overcoming this climatic obstacle. I have thought that by planting the young trees very closely together, or by sheltering them during their earlier seasons, as is done in the case of the seedlings at the model farm at Ottawa, this trouble might be gradually lessened; or, willows or cottonwood might be planted with the young trees as a shelter-belt protection for them against these early spring frosts and sudden and extreme changes of temperature. As yet, of course, we have no practical experience in the northwest on the subject, and can only base any action we may take upon knowledge obtained from what has been

done in other countries with the same characteristics both of soil and climate. (See American Meteorological Journal, 1891, Vol. VII, p. 41.)

WIND.

The effect of the wind on vegetation is quite various. Among other influences, we note the following:

(a) It is considered that the mechanical action of the motion of the stems and trunks and stalks is to strengthen them and to stimulate the growth of the roots.

(b) The winds distribute the pollen and the seed and thus assist, or even entirely control, the preservation of the plant and its geographical distribution.

(c) The wind renews the air, so that a superabundance of the necessary gases is then assured.

(d) During cool, clear nights a wind, by renewing the supply of heat, prevents the formation of frosts by radiation.

(e) On dry, cold, frosty nights the wind, by its dryness, evaporates any frost that may be formed upon the plant, but does not prevent the freezing of the plant as a whole.

(f) By bringing moisture, fog, and clouds from the lakes and ocean up over the fields and forests the wind prevents frosts and favors the growth of delicate plants on the leeward side of large masses of water.

(g) Gasparin states that when a cold, dry north wind suddenly blows over plants in active growth they become stunted, and it is said that the plants have taken cold. A similar phenomenon occurs in the valleys of California.

Gasparin's description is as follows (Cours d'Agriculture, 2d ed., 1852, p. 202):

In the valley of the Rhone the north wind produces a lowering of the normal temperature of about 7°; all the vegetation is more or less involved if after several days of calm, clear weather, during which the heat has increased, such lowering of temperature is experienced. Even if there has been no frost and the plants have preserved their vitality unimpaired, it produces a singular effect on them; their growth stops and they remain stunted. Our agriculturists describe this condition by saying that the plants have taken cold." The leaf buds which put out later resume their growth, but the leaves and branches experiencing this cessation of growth never entirely recover from it. This accident is especially injurious to natural and artificial meadows and to the leaves of the mulberry tree. As regards the meadows, the best thing to do is to hasten the mowing of the grass, in order to gain time for the succeeding crops to prosper, and for the mulberry trees it is advisable to await the development of new buds.

The more rapid these dry winds are the more they hasten the drying up of the soil. After they have prevailed for several days the earth

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becomes hard, and this condition prolonged until spring contributes much to injure the growth of the plants. The wheat remains low and does not head; the meadows yield but little grass, if a spell of warm weather does not soon follow so that they may be irrigated, for if the wind is dry and cold at the same time watering will do them little good.

(h) Damp warm winds are generally favorable to plants and particularly so to various kinds of fodder. Nevertheless, we observe that under their action the fertilizing proceeds badly, growth is imperfect, and the maturing is retarded.

() Warm dry winds produce very rapid evaporation, and their effect is still more marked if, like the simoon of Arabia, they carry with them sand heated by the powerful southern sun.

(j) Hot dry winds occur, notably along the whole eastern slope of the Rocky Mountain Divide, which by their rapid evaporation use up all the moisture in the plant and in the soil, causing the plant to entirely wilt away.

THE ORGANIC DUST OF THE ATMOSPHERE.

IN GENERAL.

The dust contained in the atmosphere, in so far as it consists of organic débris, has a slight influence on agriculture, but in so far as it consists of living germs seeking places to rest and grow it is a matter of vital importance. Undoubtedly most of the plant diseases are spread in all directions by the winds that carry the spores of fungi even more widely than they do the seeds of the weeds. But the examination of this dust, either by the microscope or by cultivation in various appropriate moist media, as also the study of the injuries or the good done by the microbes, bacteria, bacilli, micrococci, fungi, and other organisms, belongs to vegetable pathology rather than to the relations between climates and crops and is a subject so large that we must refrain from even attempting to quote the titles of recent treatises on the subject by Pasteur, Miquel, Van Tieghem, Koch, Kohn, and many other prominent authors in Europe and America. Systematic daily examination by the culture method of the dust deposited from the air had been established at Montsouris under Marié-Davy, and at Philadelphia under Dr. J. S. Billings, and will undoubtedly do much to explain the dependence of crop diseases upon wind, moisture, and temperature.

WIND AND FORESTS AND GERMS.

The influence of the forests on the transportation of the microorganisms by the wind has been studied by A. Serafini and J. Arata

by counting the collections of organisms that are caught and developed on appropriate glass plates prepared according to the methods of Miquel at Montsouris. Their observations show that in 39 cases out of 40 the catch of germs within the forest is less than the catch outside the forest, the average ratio being as 3 to 1, so that the forests act as a strainer upon the organisms carried by the wind. Wollny suggests that the result would be even still more decided if the wind were stronger and the forests more extensive. (Wollny, Forschungen, 1891, XIV, p. 176.)

ATMOSPHERIC ELECTRICITY.

IN GENERAL.

The relations of atmospheric electricity to vegetation and crops are too little understood to justify any attempt to present this subject. In fact, it does not seem clear that any appreciable influence is exerted by this atmospheric or geophysical element upon the development of plants. In natural conditions evaporation is undoubtedly facilitated by the dissipation of an electric charge, but we do not know that transpiration is at all affected by it, and have no reason to think that assimilation is affected by it. The passage of an electric current through the earth in proximity to the roots may affect the decomposition of the soil and setting free of nutritious substances or may affect the temperature of the soil. A few experiments have been made to show that artificial earth currents stimulate the growth of the plant, but. nothing has yet been found to show that under natural conditions electric currents have any appreciable influence. Nevertheless, observations are made regularly at some stations, such as Kew, Montsouris, Potsdam, and at a few agricultural experiment stations.

An excellent series was maintained for many years by Wisliczenus at St. Louis, Mo., a summary of which is published in the transactions of the Academy of Science at St. Louis and also at page 65, Report of the Chief Signal Officer for 1871. The following table gives the monthly means for Montsouris and for St. Louis. The record for Montsouris expresses the potential in units of 1 Daniell cell, which is approximately 1 volt at a point 2 meters above the soil and 1 meter from a wall, for the calm days of the years 1880 to 1887. The record for St. Louis gives the electric intensity on a scale

of arbitrary degrees for a point at the top of a house in that city for all days in the years 1861-1870:

These observations agree with those throughout the world in showing that the intensity is least in the summer seasons and greatest in the winter seasons of the respective hemispheres. There is also a corresponding slight diurnal variation, in accordance with which the intensity at a given point is least at 3 p. m. local mean time.